Best UV Sterilizer? Clear a Freshwater or Saltwater Aquarium in 4 Days

You’ve heard about the power of the ultraviolet spectrum, but should you trust your aquarium with it? Are you familiar with the basics – did you know that a submersible UV sterilizer with pump powerhead is better than one without that? I mean you have a strong flow rate on your filter, why would you want additional turbulence to your water, right? How about your setup – does that matter too? Is there a difference between the best UV sterilizer for a freshwater and a saltwater fish tank or is that one and the same thing? I’m taking the liberty to help you make the best choice, by clarifying these questions, along with your water.

Overview chart of the best aquarium UV sterilizers out there

Have a look at a short comparison chart of the models that get reviewed in this guide:

Model Link: Bulb Power: Type:
1. AA Green Killing Machine 3 / 9 / 24 W Submersible
2. SunSun JUP Series 5 / 13 W Submersible
3. AQUA UV Advantage 2000+ 15 W External
4. Jebao PU-36 36 W External / Weatherproof

Buying guidance: What you should know before purchasing a UV sterilizing unit

It’s time to bust some myths and find the truth surrounding these controversial aquarium devices. Here’s a buyer’s guide on getting the right UV water sterilizer:

What does an ultraviolet sterilizer do in the fish tank and what to expect from it?

Many water facilities are already using ultraviolet light as a means for sterilization of drinking water. It’s a common misconception circulating the Internet that UV light kills waterborne organisms in the aquarium.

That’s plain wrong.

The ultraviolet spectrum is carcinogenic. The benefits of running a UV sterilizer are rather collateral. It’s precisely this feature that fish keepers are employing when installing one such unit:

When passing through the tube the aquatic pathogens and parasites will not be directly killed. The UV bulb will actually bombard their genetic code with high-energy particles, effectively causing mutations. It will give them cancer. From there on they will be unable to reproduce with each other and therefore they will lose numbers in the water column of your aquarium or pond. The most effective wavelength of ultraviolet light is in the interval between 240 and 280 nanometers. This wavelength is known as germicidal.

Will it make the water completely sterile?

It would be an overstatement to say that a UV sterilizer will render your aquarium water completely free of vermin.

Studies have found that at any time there is a number of living microorganisms in a fish tank.

It’s overstocked with all kind of micro-fauna, way higher in numbers than if it were in the wild waters. This includes good AND bad microscopic life.

What may cause a “crash” or an outbreak is the imbalance in these numbers, favoring the harmful organisms.

A UV lamp will effectively reduce said numbers and it will prevent a possible outbreak for a variety of parasitic creatures. The reduced population density of the vermin allows the immune systems of fish to handle threats on time, encouraging the development of more antibodies.

From here, there are two takeaways:

  1. A UV sterilizer can’t treat an infection that has already started. It will only reduce the population of parasites in your water column, but it won’t take care of the ones that are already in or on your fish.
  2. A UV sterilizer will never make your water completely sterile. This includes both beneficial and harmful organisms. It will only bring in the needed stability for a safe aquarium water.

This means that if you have a “green algae soup” problem, getting a UV sterilizer is your best bet. It will make the free-floating microalgae spores unable to multiply further and they will eventually die out.

But if you have an ich outbreak that has already established itself, then you’d still need to treat your fish with the needed medication, apart from just the water.

After the infection has been treated the infant parasites will subside in the substrate.

However, upon maturity, they will leave the substrate and become free-swimming, in search of a host. This is when the UV sterilizing system comes into play, killing any mature-stage ich parasites (called Theronts).

If you have algae that’s already growing on decor and other plants and not micro-algae the UV sterilizer won’t be of help. In that case, you should first eradicate the algae through other proven methods and then run the sterilizer to kill off any free-floating spores.

If you have cloudy water thanks to microalgae (green color) or a bacterial bloom then getting a water sterilization unit will make sense. In fact, that’s one of the most efficient tools to treat these conditions. Visit the link to learn about them in detail and therefore undestand how to prevent them from coming back after the treatment.

However, if the haziness is present due to microbubbles or debris you can’t count on the UV lamp to clear it. In that case, you need some sort of fine mechanical filtration such as polyfill filter floss.

An additional benefit of using a UV sterilizer is that it will remove any traces of chlorine or chloramine. I have learned through my own experience that ultraviolet light is known to remove both chemicals from tap water.

For me, it all changed when I got my first UV sterilizing system.

Though skeptical at first, it’s now a must-have for many of my tanks.

Ever since that one purchase, I haven’t really experienced any nasty diseases in my fish tanks.

I got a separate unit for all of my tanks, eventually.

It’s really liberating not to have to worry if I’ll crash my whole tank every time I’m introducing new fish or other livestock to it. Quarantine tanks are a reasonable option here, but that’s a whole other setup to take care of.

Consider the size of your fish tank

This may seem kind of obvious, but I must say it.

For a UV sterilizer to perform well you’d need to match its power with your aquarium’s size.

If you get a weaker unit, it will need a lot more time to fully disinfect the water in your larger tank.

Manufacturers know this, so they rate their products according to how big of an aquarium they should be used on.

These ratings do not always match reality.

There are different suggestions on this matter online, that greatly vary.

I remember reading somewhere that you’d need a 25 W bulb for sterilizing a 55-gallon tank…

That’s an overkill.

I can only assume these people have never used a 13W bulb on a 75-gallon tank.

For this reason, I put together my personal recommendations for each aquarium size. Visit the link and you’ll jump straight to that (below on this page).

There, I speak of personal experience and my work with clients. I’ve had the opportunity to witness hundreds of aquariums and monitor them over time, so there’s that.

Submersible VS. Non-submersible

Generally speaking, there are two types of UltraViolet sterilizing systems – submersible and non-submersible ones. Each type has its advantages and disadvantages:

A submersible unit is considered safer as if there’s a leak, the water won’t end on your floor.

However, a UV unit can be bulky and unsightly inside of the aquarium.

Many fish keepers are quite picky about the inner aesthetics of their tank, so this may play a role in their final choice.

In my opinion, it is not a big deal, as UV sterilizers (contrary to the popular belief) should not be on constantly.

If you get a submersible one, you can simply take it out of the aquarium when it’s not running.

I’d only recommend getting an external UV sterilizer if you have a pond or a really large aquarium.

Overall, for people that own many tanks, the best UV sterilizers are the submersible ones, because of their mobility.

With or Without a Powerhead

Another thing to consider is if you’d want your sterilizer to come with its own powerhead or if it will be dependant on your filter’s one.

I highly recommend that you go for one that has its own pump and here’s a solid reason for that:

When there’s a separate powerhead the flow rate is as per manufacturer’s instructions, which is very important for the types of pathogens your UV will be targeting.

For parasites and tougher bacteria, you’d want a slow flow rate to increase the dwell time.

If there’s no powerhead the speed at which your UV sterilizer works is dependant on your filter’s water turnover.

Learn more about that in the next section.

Flowrate and dwell time

The performance of your UV sterilizer depends on the dwell time of the microorganisms. The dwell-time is defined by:

  • The flow rate of the pump that forces water into the tube
  • The size of the tube
  • The Wattage power of the UV bulb

Generally, it goes like this:

At a slower flow rate, the pathogens are exposed for a longer time to the UV light. This reduces the numbers of parasites, and more resilient bacteria and microbes.

At a higher flow rate, there’s less time for the organisms to be exposed to the bulb’s destructive radiation. Such flow rates are recommended for the “green algae soup” syndrome. Microalgae spores are not as resilient and they can still be eradicated with a higher GPH.

As you can see, control is everything here.

Usually, in larger aquariums, the need for filtration is greater, because they’re housing larger, messier fish.

The common practice is to employ a canister filter, as they provide higher flow rates, among other advantages over Hang-On-Back filters.

In such systems, it’s normal (and healthy) to have the water turnover at 6 to 8 times per hour, which often equals more than 600 GPH.

This turnover, however, would often be too much for a UV sterilizer to do its job, unless the bulb is really strong.

A very strong bulb shortens the dwell-time needed for parasites to get seriously damaged.

That being said, we can conclude the following:

  • If you seek a UV sterilizer for a larger aquarium (think 55+ gallons) you’d want to get one that has its own powerhead.

    This way you’ll be able to control the flow rate as it is described by the manufacturer. It will also allow you to get away with a “weaker” UV bulb because you will control the dwell-time.

  • Whenever a UV sterilizer doesn’t have its own powerhead this means that it’s dependant on your canister filter’s flow rate.

    This is often a high GPH rate, which imposes the need for a very strong UV bulb as without a powerhead that’s the only way you control dwell-time. High-Watt bulbs cost significantly more, sometimes hundreds of dollars.

So, this is where the myth of having to purchase high-Watt UV sterilizers originates from.

It’s why you’ll see some sterilizers rated at, say, 100 gallons while having just 15W of a bulb. Where others may be rated at less while equipped with a more powerful lamp (and coming at a higher price).

In truth, if you manage to find one that has its own powerhead, you can cut the cost of expensive bulbs that will also need changing over time. Which leads me to the next section.

Investment over time

Let’s be honest here.

You will need to change the bulb over time, but that’s not a short period.

If you use your device often and every day you will have to change the lamp every 6 months or so.

I run mine every couple of days for no more than a couple of hours.

This is more than enough for me to prevent any outbreaks while saving bulb-life.

There are some units that get super expensive and you’ll hear that they’re recommended for your tank’s size.

Not the truth in my humble observations.

You can absolutely get away with a water sterilizer for under $100 if you don’t own a decently sized pond or aquarium (think over 150 gallons).

The investment is absolutely worth it, especially when it comes to sensitive marine life.

In reefing, one could lose hundreds of dollars worth of fish in the course of days, just because of a single outbreak.

This does not mean that you’re safe if you own a freshwater aquarium though…

I run such units on most of my freshwater aquariums as well, because nasty parasites can inhabit both salt and fresh water.

Does a UV Sterilizer eliminate Beneficial bacteria as well?

The wavelength of the ultraviolet spectrum is not picky, it will destroy anything that gets irradiated by it. It will not spare the good while getting rid of the bad. However, this is not the full answer to be had here. Here’s what happens to your beneficial bacteria when you run a UV water sterilizer in your aquarium:

The beneficial bacteria live on a surface area such as substrate, decoration and the biological media. Since it is not free-floating in the aquarium’s water column, a UV sterilizer won’t be able to kill the established bacterial colonies.

Note that if your tank is not fully cycled yet, there’s a chance that a great portion of the beneficial bacteria may still inhabit the water column.

It’s why it is not recommended to sterilize the water with UV light, during nitrogen cycling.

“But what about phytoplankton and zooplankton in reef tanks?” – the concerned reefer would ask.

The answer is pretty much the same:

The UV sterilizing bulb will probably kill anything that passes through its tube non-selectively. However, copepods and crustaceans, for example mostly inhabit the surface of live rocks so they will not be notably affected. You may have to dose a little more phytoplankton, but that’s a fair trade, knowing that there’s a significantly smaller chance of an outbreak in your reef tank. Just be sure to turn the UV off, while feeding the tank.

The best UV sterilizer for saltwater reef tank would be the one that runs on a proper schedule. You can learn about that in the “tips for usage” section below in this article.

What is the best UV sterilizer for clearing the water in a fish tank?

There’s no distinction between a UV sterilizer for freshwater aquarium and a reef tank. The effects of ultraviolet sterilization on water have been proven throughout years of research. All models in the reviews below will work for both setups. Have a look at the best UV sterilizers for clearing aquarium water:

1. AA Green Killing Machine 3W/9W/24W – Very Efficient & Decently Priced

Click to see the current price + MORE photos on Amazon.

This is my personal favorite. I’ve used this on a LOT of my freshwater fish tanks with phenomenal success so far.

What drove me to purchase it was the huge amount of positive user feedback.

What I really like in the Green Killing Machine (appropriately named) is that there’s no external plumbing work. Simply, I unpacked the stuff and hung it in my aquarium.

The UV bulb chamber is submersible.

The installation took me just about 5 minutes as per advertised.

That’s apart from reading the instructions though.

There’s a part of the device that should not be hanged over your aquarium water, so make sure you read them carefully.

It has its own powerhead, which eliminates complicated calculations of GPH for the best performance.

Now about the work this UV sterilizer does.

The 9W version managed to clear the haziness of my tank’s water pretty fast (something like 40 hours or so).

I used it for a bacterial bloom, which made the water pretty cloudy.

My tank was planted but by following a schedule, this UV sterilizer performed well, without interfering with the fertilizers.

I used the larger 24W version on my bigger tank for green water.

The story:

My 125-gallon tank was so densely populated with microscopic algae that I could barely see anything that was 3 inches further from the glass.

I was at my wits end so I decided to give this guy a try, after seeing its lighter version clearing the water in my smaller tank.

I went ahead and ordered it online.

From there everything changed.

In just about 3 days, if I remember correctly, the water in my large tank was back to normal.

Not even normal, actually. It looked pristine.

I now run the units just as a precaution measure.

I run them every 3 to 4 days for about 5 hours.

Haven’t had any outbreaks of bacteria, parasites or micro-algae ever since.

I’m very happy with this brand of sterilizers.

The 24W version can handle fish tanks of up to 180 gallons.

No joke, the Green Killing Machines are worth every penny (in fact, I think they’re underpriced).

Drives me mad that I didn’t try it earlier.

 Advantages: 
  • Super-fast installation
  • Has its own powerhead
  • Sturdy design
  • Special UV bulb chamber for an extended dwell-time
  • No work with external plumbing
 Disadvantages: 
  • The suction cups don’t always hold well from the first time
  • You can’t control the flow rate (the manufacturers claim that’s on purpose, and it does seem to work, so I’m somewhat fine with that)

2. SunSun JUP-(xx) 5W/13W – Fantastic for the Price

Click to see the current price + MORE photos on Amazon.

Apart from having their own canister filter with a built-in ultraviolet sterilizer, SunSun is a very reputable brand when it comes to independent sterilizers.

I’ve found the JUP-02 to be a very reliable addition to most of my small-to-medium sized tanks.

Their JUP series come into play with larger tanks as well.

The JUP-23 is what I recommend for a 75-gallon tank, for example.

You can read more on that in my personal recommendations section below.

Both units will perform best for the adequate aquarium sizes I’ve mentioned.

The build of these units is pretty simple.

The instructions are somewhat vague, but it’s pretty much “plug and play”.

What I also like about this UV sterilizer is that it has its own powerhead and it’s completely mobile.

You mount it in about 5 minutes, turn it on and that’s it.

Thanks to the adjustable flow rate, I could set it to whatever GPH I wanted, as per manufacturer’s instruction.

Assuming that you’ve read the buyer’s guide above, you already know how important a controllable water turnover is with these units.

I would like to mention something important here.

Many reviews of this unit claim that the UV is sometimes too strong and melts down the plastic. Here’s how I run them and haven’t had any problems yet:

At the initial green water clearance, I would run them 12 hours at a time for as many days needed, for the haziness to go away. After that, I would run them every other day, and sometimes every third day for about 5 hours or less at the slowest flow rate possible.

I’ve had both units for some time now, and I did not experience any plastic meltdowns.

Just keep my schedule in mind when you get your own.

The SunSun JUP series UV sterilizing units are a great investment.

I happen to run mine in freshwater aquariums, but you can absolutely run them in your reef tank as well.

 Advantages: 
  • Adjustable flow rate
  • Mobile unit with a fast setup
  • Super competitive pricing
 Disadvantages: 
  • Instructions may not be clear ( Watch this video instead. The guy is not super handy but manages to show how it’s done)
  • Should not be run more than 12 hours per day, because it may melt its own plastic

3. AQUA UV Advantage 2000+ 15W – Durable & Sturdy

Click to see the current price + MORE photos on Amazon.

As the title goes, the AQUA Advantage Series are very durable and reliable units.

This one does not come with its own powerhead.

As much as I’m a fan of UV sterilizers that pump water on their own I’m pretty happy with this one’s performance so I included it anyway.

It’s of high quality and it clears the water like a beast.

You can either plumb it in the return water line of your sump or on the outtake of your canister filter.

The whole plumbing thing is not rocket science and, fortunately, it has been made so that everyone could assemble it on their own.

Now on to the performance.

The higher Watt bulb allows for a better sterilization, but that’s necessary since the unit is meant for larger aquariums where the flow rate is also higher.

This equals shorter dwell time unless your canister filter or whatever filtration system you have has an adjustable flow.

Still, the UV bulb is particularly durable and strong enough to handle aquariums of up to 125 gallons in volume.

I’ve run this on a 90-gallon freshwater tank and it did an outstanding job at clearing the water.

The canister I was running was a SunSun HW304B, which claims to turn the water for 520+ gallons per hour.

That, however, is not realistic (from my observations) and it actually turned around…350 GPH.

Which was still quite a lot, plus I ran 2 of these simultaneously.

Anyway, the Advantage 2000+ did its magic – the water got perfectly clear and no bacteria, algae or parasite outbreaks were had ever since.

A “con” I would like to mention if I can call it that way, is that the hose of your filter may not always fit with the unit.

In that case, you’ll simply have to buy an adapter.

Hardware stores will have the fittings as they are pretty generic.

Just an extra walk to the store, that’s all.

Overall a very sturdy unit with a huge potential. I like and recommend to fish keepers with above-medium sized aquariums.

 Advantages: 
  • Durable design is manufactured in the US
  • UV bulb is one of the most durable ones I’ve personally seen
  • Easy installation, despite being an external sterilizer (here, have this video for the setup)
 Disadvantages: 
  • May need adapters to fit with your filter’s hose
  • No powerhead, flowrate will depend on your filtration system

4. Jebao PU-36 UV sterilizer 36W – For Large aquariums & Ponds

Click to see the current price + MORE photos on Amazon.

If you have a pond of your own you are probably familiar with the Jebao equipment.

They make quality gear at very reasonable prices.

Their UV sterilizers are not an exception (here’s their 9W TotalPond UV Clarifier that’s absolutely crushing it when it comes to smaller ponds).

This 36W UV unit is the beast in this list.

It’s like the Hulk. It’s bulky and it destroys your aquarium’s enemies.

It’s designed to be used on very large fish tanks (of over 200 gallons) and it is not a submersible unit.

It does not have its own powerhead, but that’s understandable, given that you’d definitely need separate filtering systems for such sized bodies of water.

There’s no need of adapters, as it comes with variously-sized fittings for tubing.

The manufacturers claim that it will tolerate up to 4400 GPH.

The water inside of the chamber travels in a spiral around the UV bulb, maximizing dwell-time.

It’s actually very durable, despite its very competitive price tag.

I do not currently own an aquarium that’s 200+ gallons, but I have personally seen this device in work.

It can definitely handle heavily algae-infested ponds and aquariums spectacularly fast.

From a couple of fish keepers, I have seen using it, I can conclude that it clears roughly 100 gallons of water a day.

And by that I mean, it makes the water crystal clear over that period.

If you have an exceptionally large aquarium or a decently-sized backyard pond, then this should be your pick for a healthy water.

Mind that if you use it outside, you shouldn’t run it during the cold months.

The Jebao PU-36 is the best ultraviolet clarifier and sterilizer for large aquariums, in my opinion.

 Advantages: 
  • Best bang for your buck
  • External – it does not interfere with your aquarium’s inner aesthetics
  • Special bulb chamber design for maximum dwell-time
  • Can handle extremely large volumes of water
  • Durable build
 Disadvantages: 
  • It’s bulky
  • The instructions are outright garbage ( It’s really simple though, watch this guy’s video and you’ll get the hang of it)

UV sterilizers for differently-sized aquariums

The above reviews are an overall evaluation of a certain unit. However, now it’s time for me to give you some suggestions on where and how to use them. Here’s what size of an aquarium suits these UV sterilizers best and which particular product you need for yours:

Top UV sterilizer for a 5-GALLON aquarium

For a 5 gallon tank, I wouldn’t recommend using a UV sterilizer unless you’ve already tried everything else. The reason is that these devices will take some room in such a small tank. In such case, it is best to run one until it clears the water and then, remove it. For this task you’d need something with no more than 3W of a UV bulb, that is submersible:

The perfect candidate is this.

This magnificent little thing will definitely kill any free-floating algae spores and parasites that are populating your small tank.

It’s rated for up to 36 gallons per hour, so it may add up somewhat of a turbulence in the tank.

Note that if you have a Betta with large, beautiful fins, it may experience some difficulties swimming around.

This may cause the fish to lay around more from the exhaustion (which is a normal behavior when facing a stronger current).

For this reason, I recommend that you use this sterilizing unit only when needed and not all the time.

You won’t regret it, just mind the time it is running.

I would not keep it on for more than 12 hours a day.

Top UV sterilizer for a 10-GALLON aquarium

In a 10 gallon aquarium it is really best to have a sterilizer that has its own powerhead:

Having 3W of UV power would be more than enough for such a setup, given the flow rate of the device is decent. A good unit, in that case, would be this one.

It’s an internal UV sterilizing system that will do its job as it’s rated for up to 20 gallons.

The water turnover of the powerhead is ideal for clearing up such volumes of water (around 37 gallons per hour).

The product is about 7 inches in length and roughly 2.5 inches in diameter so it fits a 10-gallon fish tank nicely.

Top UV sterilizer for a 20-GALLON aquarium

To be honest the above recommendation ( AA Green Killing Machine, 3 Watt bulb ) would be sufficient for a 20-gallon fish tank as well:

This UltraViolet sterilizing device fits in the 20-gallon range upon manufacturer guidelines. If it’s not your only water turnover unit you’ll be perfectly fine eradicating the harmful pathogens and microalgal blooms in your fish tank’s water.

From what I’ve seen with clients, you should be set, with a crystal clear water in less than 2 days, or in some heavy “green water” cases – 3 days.

Top UV sterilizer for 30 and 40-GALLON aquariums

If you have either 30 or 40 gallons of a fish tank (or a pond for that matter) you’d want a sterilizer with roughly 5 to 7 Watts of bulb power. For these two particular cases I’ve seen a fantastic result with a 5W UV bulb:

The device I used on my 40 gallons was this one (link will show you some photos on Amazon).

It thoroughly cleared my water that had turned into a pea-soup color in just about 3 days, If I remember correctly.

From dense green where I couldn’t see the other side of the tank to super clear and transparent.

From then on I occasionally ran the sterilizer every 3 to 4 days for about 4 hours, which seemed to provide enough UV sterilization.

I’ve never had this happen to my 40 gals again, actually.

The adjustable flow rate of this device will allow you to fine-tune what you’re battling against (as mentioned in the guide above).

Top UV sterilizer for a 55-GALLON aquarium

To best sterilize 55 gallons of water and efficiently reduce the harmful microorganism colonies that inhabit it you’d need something between 7 and 10W of a UV bulb:

The perfect solutions here would be this such one UV sterilizer.

It’s currently dominating the market and for a reason.

Frankly, the 9 Watt version is among the best budget-friendly yet super productive sterilizing units at the time of writing.

Though it’s rated for up to 50 gallons, it will do an outstanding job in a 55-gallon aquarium.

It shows noticeable results fast and you don’t need to run it 24/7 when using it as a preventive measure.

I am a huge fan of these units, and I personally own 2 of them (one 9W and one 24W for a larger tank I have).

It’s reasonably priced for the job done, so I would say it’s absolutely worth it.

By the way, going through the Amazon reviews, you may find that many users say that you shouldn’t purchase the 9W version unless your tank is 40 gallons or less.

My experience, along with my crystal clear water on the 55-gallon I have shown otherwise.

It will do the job, so no need to pay extra cash.

Top UV sterilizer for a 75-GALLON aquarium

If you want to sterilize the water in your 75-gallon tank in a matter of days you’re looking into getting a UV bulb that’s 13 to 15 Watts:

I good recommendation I can give here is this 13W UV sterilizer.

Honestly, you’ll probably have your tank water cleared from its green colored water with a less powerful 9W UV bulb as well.

However, it will take weeks, and you would not be able to efficiently control parasites with a lower Wattage.

So as the title goes, you’ll clear 75 gallons of water with this unit in a matter of days.

I have personally witnessed this sterilizer take care of a can’t-see-through algae soup in just about 3 days.

The fourth day the water was still partially cloudy, but not green by any means. At the beginning of the 5th day, it was completely clear, as if there was no water at all.

You’ve probably noticed the price tag by now.

The SunSun are quite famous for making inexpensive yet effective equipment overall, not just UV sterilizers.

Since this unit has a controllable flow rate, I’d suggest keeping it at the lowest possible rate, after initially clearing your water.

This way you’ll keep parasites and harmful pathogens in check.

Don’t run it every single day.

This way you’ll prolong the lifetime of the bulb.

Turn the sterilizer on every 3 days or so for a couple of hours (my success has been with keeping it on for about 4 hours a day).

Top UV sterilizer for a 90-GALLON aquarium

For clearing the water in your 90-gallon fish tank you’d need between 15 and 18W of a UV bulb.

We’re scaling the Wattage because the bigger the tank gets, the more flow is needed to maintain its full capacity under protected from harmful organisms.

The higher the flow rate, the more UV power you want, because the dwell time (time in which the microorganisms are exposed to the UV in the tube) gets reduced.

In this case, a 15 to 18 Watts bulb compensates for the naturally higher flowrate with its raw power.

Now on to the product for this section:

A reliable UV sterilizer that has the right flow + Wattage would be this one (Amazon link for photos and its current price).

The AQUA Ultraviolet is a beast in the industry, that along with being really efficient, comes with extra durability (for some reason).

I say “for some reason”, because, at first, it looks cheaply built, but you can actually use it for years to come.

It has a slightly higher price on it, though I can confirm that’s justified.

This particular UV sterilizing unit can be used for tanks that are up to 125 gallons with great success.

This one, unlike the ones I recommended so far, does not have its own powerhead, so make sure that you plumb it in your filter or pump’s outtake.

The mounting is easy, just follow the manufacturer’s instruction.

An absolute beast, that I actually own and am pretty happy with.

Top UV sterilizer for a 125-GALLON aquarium

Sterilizing 125 gallons of water is not an easy task unless you buy the right equipment. Here’s what I’ve found works for me:

You could absolutely use my previous recommendation here. Though it’s a smaller Wattage, this UV sterilizer’s design and size are made to serve large aquariums.

It will successfully solve your green water problem while getting you rid of harmful organisms in the longer run.

However, it’s not what I run on MY 125 gallon.

On my tank, I run this.

Reason being that I was super happy with the 9 W version. This, larger one, despite being 24W is rated for up to 100-gallon fish tanks.

Anyway, I really wanted to try the scaled version, so I asked around and it turns out many were using it not only on their 125s but also on up to 180-gallon aquariums.

So I went ahead and purchased the thing because I wanted to keep my AQUA Ultraviolet for my other smaller tank.

Oh, boy, am I glad that I did.

This thing (the GKM) worked perfectly, made my water crystal clear, and I’ve never had a “crashed” tank after getting it.

Turns out it’s a low-cost alternative to other, more expensive brands, and it actually does the job.

It has its own pump, making it way easier to install and you don’t really have to calculate flow rates. Simply enjoy a healthy water.

I’m a die-hard fan of this device and would recommend it to anyone in doubt (which happens often, because of people being skeptic towards the magic power of the UltraViolet spectrum).

Let’s summarize:

If you want to have a disease-free large aquarium and keep your expensive fish healthy for the rest of their days, buy this unit and call it a year.

Top UV sterilizer for a 150-GALLON aquarium

A UV sterilizer that will best fit and clear the water of a 150-gallon tank would be the Green Killing Machine 24W:

As I mentioned in the above section (I suggest you read that if you just jumped straight to here) this sterilizer will perform fantastically for this range of water volume.

The UltraViolet bulb is as durable as it gets and you should probably run it on a timer after killing off the initial microalgae bloom.

I run mine that way, and I don’t keep it on for more than 5 hours as a precaution for algae blooms or parasites.

The pump comes with a 3-year warranty and the bulb should be changed every 6 months.

That’s according to the manufacturers, with a daily usage implied.

I’d like to think it’s smart of me to run it every couple of days instead so that I prolong the bulb’s life for about a year or so.

It’s been almost a year since I got mine and it’s still running like a beast, no bulbs changed yet.

An overall great product, in my opinion. I can totally vouch for this UV water sterilizer serving your 150-gallon tank well.

Top UV sterilizer for a 180-GALLON aquarium

To clear the green from your water in your 180-gallon aquarium you’d need between 24 and 30W UltraViolet water sterilizer:

In that case, the aforementioned recommendation will do. The Green Killing Machine 24W is powerful enough to clear the water of 180-gallon fish tank in just about 4 days.

It is also powerful enough to keep your water free from parasites from then on.

The size of the UV sterilizer is not of importance here, but rather the power of the UV light combined with the time of exposure.

Install it and wait out for a couple of days. After the water gets crystal clear all the microalgae will be dead.

Now you’d want to occasionally run it every couple of days, to ensure a dwell-time to which parasites are exposed to the ultraviolet spectrum.

This way you’ll be able to keep your tank or pond’s water vermin-free. This includes other harmful pathogens too.

Seeing how efficient this unit is over my 125, and also in the hands of clients I’ve recommended it to (owners of 180-gallon fish tanks or ponds) you can rest assured that it is well worth every penny.

And given how high the pricing on UV sterilizers can get, that’s not a lot of pennies, while still getting the work done.

I recommend.

Top UV sterilizer for a 200 OR MORE GALLON aquarium

For a 200-gallon fish tank we’d need to scale up the wattage:

Honestly, the above recommendation might work for clearing your “pea soup”, but it will take longer.

If my calculations are right, by using the Green Killing Machine’s 24 Watt light bulb would take around a week do destroy any traces of microalgae, which is okay.

If that’s your end goal – buy it and be done with it (visit the link to see more details on Amazon).

However, if you’d like to be able to protect your aquarium or pond from future outbreaks of parasites, you’d want a stronger bulb.

I can suggest something that I’ve seen work for aquariums and ponds that were over 200 gallons, actually:

It’s this. It’s a Jebao with a 36 Watts of ultraviolet sterilization.

I’ve witnessed this monstrous UV clear a 200-gallon tank in 2 days.

I’ve also witnessed it make the water of a 700-gallon pond crystal clear in just about a week.

It’s an external UV sterilizer, not submersible. Do not submerge it underwater, and as the manufacturers suggest install it after the outtake of your pump/canister filter.

That’s a good tip for any water sterilizer out there, as this way they’re only targeting microorganisms and not gunk or debris.

Be it 200, 300 or even 500-gallon tank, this unit will do its job, without breaking the bank.

I am kind of against hundreds of dollars worth of aquarium equipment, especially in this field (water disinfection).

Most “cheaper” units will absolutely do the job and this device is the perfect example for that.

By the way, I consider getting 2 units being extra careful. If I were you I’d only resort to that if I had a body of water that’s above 600 gallons in volume and is super overstocked with fish.

Some people report having cleared their ponds of over 9000 gallons with this unit. It’s that strong.

Tips for proper usage of a UV filter unit

To ensure optimal performance when using your UV sterilizer you should:

  • Install it after your filter or pump’s outtake. Aquarium water is densely populated by microscopic organisms, while high on other organic and non-organic matter. This means that some of the intruders you’d want to zap may ‘hide” behind the mass of other bacteria or debris. By installing the UV sterilizer right after the return line of your filtration system you are making sure that no debris will compromise the reach of the UV light.
  • Use with filter floss for a crystal clarity. Fine filter floss, such as quilt batting will make your water pristine on its own (look up my article on that in the Search bar). When combined with a UV sterilizer you will achieve a 100% transparent look, along with reduced chances of illness or an outbreak.
  • Don’t use during nitrogen cycling. Beneficial bacteria live on the surface area and not in the water column. When the tank is still cycling, however, the population will still be sensitive and therefore imbalanced. There’s a chance that you’ll reduce the numbers of other organisms that help the establishment of nitrifying bacteria. After you turn off your UV unit, you can use bottled bacteria to ensure stable colonies of beneficial nitrifiers.
  • Run it on a schedule. To run a UV sterilizer 24/7 would be an overkill unless otherwise stated by the manufacturer. A good disease-preventive schedule would be to run it every 3 to 4 days for no more than 5 hours.
  • Turn it off while feeding your corals. Since coral food is free-floating organisms, there’s a high chance that your UV sterilizer will decrease the value of the meal. Running it in a reef aquarium will never sterilize your water from beneficial phytoplankton, but you will have to add a little more food for your corals than usual. It’s well justified to spend a little more on food than hundreds of dollars for new fish every couple of months, because of a crash.
  • Turn it off while dosing fertilizers to your plants. The UV light may alter the chemical structure of the fertilizers, so you should not run it constantly when dealing with a high-tech heavily planted aquarium. If you follow my recommended schedule you will be completely fine.
  • Clean the glass sleeve. The glass sleeve is where the gunk of dead bacteria and other pathogens will accumulate. As every other degrading matter, this may cause a spike in nitrites or ammonia if left for too long in the fish tank. Clean it every month or so.
  • Never use it with medicine. Most chemicals can also be broken down by the high-energy ultraviolet photons. Running your UV sterilizer along with medicine in your tank is not a good idea. It may render the medicine useless or even worse, make it toxic.
  • Change the bulb when the time comes. Otherwise, you’ll only waste electricity. These are special UV bulbs that do wear off.
  • Control the flow rate if possible. I may be repeating myself, but a slower flow rate increases dwell-time, ensuring damage to the more resilient parasites, bacteria, and fungi.
  • Monitor the water temperature. Logically, a strong UV-C lamp will give off some heat. These devices do raise the temperature in the aquarium, but that’s with a mere degree or two. The only time you should be concerned with that is during the extremely hot summer days, where some sort of cooling may be needed. My secret weapon for this kind situation is my air-conditioner.

A light conclusion

Choosing the best performer among the many UV sterilizers is actually quite simple, as long as you know your stuff. I hope that these reviews and additional guidance gave you the info you were looking for.

What model did you choose in the end? Is your setup freshwater or saltwater? Do you want an additional recommendation? Ask your questions in the comments and I will get back to you as soon as I see them.

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Jeratt Wollner
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Jeratt Wollner

Great information here, thank you so much.

Just wondering what size of pump should a guy get for the “Jebao with a 36 Watts”?

I would be using this in a hydroponic application, in my water storage tank before adding nutrients and feeding to my plants.

Thanks again for your help.

Kostas
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Kostas

Hello what if i use more watts for lower gallons will this do the job quicker? Is there any side effects on that? Ofc will have it few hours per day.