Tips (+Gear Suggestions) for Buying the Best 125-Gallon Aquarium Light

Having a 125-gallon fish tank is presumably the next level of fishkeeping and, boy, can it be rewarding. However, finding a 72 inch aquarium light can be outright challenging. With such tank dimensions, the right fixture size becomes the trickiest part. Moreover, I know how keeping light-dependant livestock in such a big space can get complicated. So which fixture classifies as the best lighting for 125 gallon reef tank, for example? What about freshwater planted tanks? I think I can help.

QUICK NAVIGATION:

I. Essentials of a Light for 125-Gallon Fish Tank

II. Factors to consider before buying a light fixture for a 125-gallon tank:

  1. Type of Light Source
  2. Produced Heat
  3. Size of the Light Fixture (Product Examples)
  4. Intensity Control
  5. Timer

II. What to pick according to your fish tank setup:

  1. 125-Gallon Reef Tank
  2. 125-Gallon Planted Tank:

What to look for when buying a 125-gallon aquarium lighting?

The spectrum of light coming from your fixture of choice should include all life-supporting colors. Having a red light source has been confirmed to favor fish appetite and plant growth. But what else? In general, here’s what plays a major role in choosing the best light for a 125-gallon aquarium:

When covering 72 inches of the water surface in a 125-gallon aquarium the size of the lighting unit is among your greatest concerns. The dimensions of the fixtures have to accordingly fit the tank (72″ x 18″ x 21″). Illumination area should eliminate corner shadowing and the “beam-light” effect. Light intensity along with the right lensing dictates what type of corals or plants can be grown. For different aquarium setups, different lighting choices will be appropriate.

Below, I will mention what brands have worked for me. Click the link if you want to jump to that.

Factors to consider when picking a light for a long (125 gallon) fish tank?

Here’s a detailed list explaining what you should consider when picking the right light for your 125-gallon aquarium:

Type of light

One thing you need to decide on is the type of lights your particular fish tank setup would need. Depending on the livestock and aquascape you want in your tank, different suitable light sources can be considered. Generally, you can choose among the 3 types of aquarium lights:

  • Fluorescent bulbs – I started fishkeeping a long time ago. Lighting options back then were pretty much limited. Throughout my years of setting up tank after tank, I’ve found that fluorescent lights can be a pretty good choice for any type of aquarium. The full-spectrum bulbs are novice-friendly as they’re suitable for plants, corals and fish alike.

    I’ve also had success with 50/50 white actinic lights in my reef tanks before. The combination worked because the Actinic light is light that leans toward the blue spectrum, which is perfect for coral growth, and the white light would just make my tank pleasant for the human (my) eye.

    There are also specialized fluorescent plant bulbs. These would simply provide anything a heavily planted freshwater aquarium would ever need in terms of photosynthetic activity.

    The pros here are quite obvious, I think – in general, the tubes are easy to find, I could say cheap and there are a variety of formats. There are different “T”-diameters such as T5, T8, T12 etc. The digits in the name stand for how many eights of an inch the diameter corresponds to. A T5 means that the diameter is 5/8 of an inch where a T8 would respond to a diameter of 1 inch. Usually, it’s a wise move to go for the T5’s, instead of the T8’s as they are more compact and last for as much as 20% longer. However, this may not be the case for a 125-gallon tank…

    The main drawback of these is the constant maintenance they require. Even with a high-end top of the notch set, you’d need to buy bulbs annually (or even more often), because with time they lose intensity. For a 125 gallon, it may get costly as you’ll either have plenty of bulbs to change or you’ll have serious difficulties finding the 72″ long ones. The bulbs would also produce enough heat for you to consider a chiller, which is even more money wasted. There’s also the electricity bill. In a long-run scenario, I honestly can’t recommend these for a 6ft long aquarium.

  • HID or High-Intensity Discharge lighting system metal halides – Metal Halide lights are a pretty genius invention, according to my limited knowledge. The idea is that when electricity passes through a container of halide salts and gas, the tube starts producing a really, really intense light. What this means is that we are absolutely capable of satisfying our high lighting requiring plants and corals without spending a fortune on electricity bills.

    A reef tank with metal halide lights is not uncommon. These light fixtures are also used for deep aquariums (over 24 inches) as their illumination penetrates the water mercilessly, right to the bottom of the tank.

    Another really great thing about metal halids is the shimmering effect they give out. The one that mimics the natural light in the ocean. However, a 125-gallon fish tank is a little over 20 inches deep and the rather expensive bulbs may not fit your budget…

    Disadvantages are not absent when it comes to metal halides. Remeber how I said they are super-intense? Well, the heat they produce is also super-intense. Metal halides can become scorching hot and a chiller is a must here. My room would become a radiator on its own when they were on. I was not okay with the thought of them being hotter than my wife…

    Same as the fluorescent lamps, metal halide bulbs will also need a replacement with time. Although not as often it can still be often enough to become wallet-sensitive. Despite being a popular choice among reef keepers I’ve found that under metal halides some of my corals do not show their full color potential. Another minus to having MH is the color customization – something that is really important for a reef tank.

  • LED or Light-emitting Diode lights – With LED fixtures you can expect a fine-tune in color customization, very low to none heat produced, an unmatched product life and functionality in the form of dimming and whatnot. LED lights have a water penetration that is, in my opinion, better than an MH’s one.

    They are a ton brighter for the same power consumption, which has resulted in an electricity bill close to 4 times smaller than before, for me. You will not have to worry about light changes with LEDs, as they have an estimated life of 50,000 hours while working. Even if you’re nuking your aquarium with the brightest light setting for 10 hours a day, that’s still well over 12 years.

    The color rendition with LED fixtures is a breeze. It can be a gamechanger for reef aquariums. Me personally, I like my corals as colorful as possible. From what I’ve observed after switching from MH to LEDs I guarantee you, you will see colors in your corals you never thought existed there. The growth will be the same if not better under this type of lighting. This applies for my freshwater tanks too – there’s nothing like a beautifully complimented colorful fish.

    Another thing I fancy about LEDs is that there is no need for a chiller, I just run them and leave them as they are. I do not need to worry about turning my home into a blazing inferno now.

    The cons of LEDs are their initial cost. Keyword here being initial. In the long run, they will still save you, dare I say, thousands of dollars. However, the initial cost has been rapidly decreasing over the past couple of years, because of competition and an increasing demand. So it is not THAT much of a difference, in my opinion.

    The other thing I would hardly consider a con, but am still obligated to mention is the PAR output. And by that, I don’t mean they have a low PAR output, but just the opposite, it is confusingly high, even more than a metal halide’s one. See, PAR stands for Photosynthetically Active Radiation. That’s the radiation with a waveband between 400 and 700 nanometers, which is the one required for photosynthesis. It falls between ultraviolet and infrared light on the electromagnetic spectrum, with 400 being the beginning of the ultraviolet. LED lights use “Royal Blue diodes” that are super efficient in that 400-nanometer department. So efficient, in fact, many fishkeepers make the mistake to miscalculate PAR values and unintentionally “fry” their corals in the beginning after switching to LED lighting. Me included. Now I know LEDs need to give off considerably lower PAR than metal halides. So the disadvantage here is the needed time for adjustment and acclimatizing for plants and corals. But this is pretty much where the disadvantages of LED lights end.

Heat

Light bulbs can be deceiving in their potential to give off heat. Ever made the silly mistake to try and remove a bulb in your hallway just seconds after you turn it off? Being my usually distracted self, I have. They get as hot as hob plates. Now imagine a special light bulb designed to stay on for 10 hours a day.

Metal halides give off the most heat of all three types of lighting. This can heat your aquarium water, which can be quite the issue in the summer. Chillers are not the cheapest of equipment either. I get that we are all hobbyists that are willing to spend a little more on our passion, but blindly wasting money is another thing.

One of the secrets to the LED lighting longevity is the way they manage heat. They have a special heat sink from where the heat leaves. This results in LEDs having a lifetime times upon times longer than the usual fluorescent or metal halide bulb. All that without the need for chillers or fans.

Size of the light fixture & Even spread of the light

Getting the right size of aquarium light for a 125-gallon tank with measures of 72″ x 18″ x 21″ can quickly become frustrating. Finding a fixture that is 6 feet long can be very difficult indeed.

If you intend to have a FOWLR or FO aquarium (which I doubt, if you’re at the stage where you consider having a 125 gallon, but hey) one 60″ fixture MAY be enough. In general, live rocks and fish don’t care that much for a specific lighting. Your only concern here would be what type of light will best compliment the colors of your livestock.

However, plants and corals do care. A lot. If that is the case for you I wouldn’t recommend compromising with the size of the fixture. It has been my experience that a couple of smaller units with a little adjustment can eliminate the shadowing problem in the corners.

For example, on my 125-gallon reef, I use 165W MarsAqua LED fixtures. You can check them out here on Amazon if you’d like. I ended up buying those because of how efficient they are for the money and couldn’t really risk it with my reef tank.

Anyway, each unit is 15.8 inches long, which means that 4 would nicely cover my whole tank, with very small – 2″ – gaps in-between them. This is now the case. However, when I started my reef tank, I only got 3 of them, because of my limited budget. Yeah, 3.

The reason I went with that number was that I’ve found a really sneaky solution to make up for the 6″ gaps in-between them. The said solution worked absolutely trouble-free for me.

LED lights come with lenses that are used to concentrate the lights from the diodes. With the lenses, the light is more of a beam and there is not that much color mixing. To avoid spotlighting I slightly “modified” my lights by removing (all or some of) the lenses. This is quite important for plants, corals and the overall aesthetics of your tank. By removing the lenses you will lose some intensity but get an even light spread. LEDs are also pretty intense so this would not be an issue.

Luckily, 125 gallon aquariums are not deep by the fishkeeping standards. Generally, any aquarium that is not over 24 inches deep would not need lensing, because of how intense and penetrating LED lighting can be. After removing the lenses you should gradually increase the intensity and experiment to see how the aquarium inhabitants react.

On LED lens removal – I consider myself a medium-handy guy, but this DIY “project”, if I can call it that, can be handled by anyone. If you haven’t done such thing – don’t worry, it’s super simple. All you need is a screwdriver and 20 mins off your time. Just remove the screws of the lighting box, and carefully lift the top. Set the top aside. Inside you’ll find another plate, on which the diodes are mounted (facing downwards). Remove the screws from this one as well and you now have access to the diodes. From here on, you just manually unplug them, as you try to be gentle. Here’s a video of some guy doing so:

I removed all of the lenses on my outer pieces, but if you plan on having an SPS coral dominant tank (the ones that require high lighting) you can leave a couple of lenses in the middle. As I said in an aquarium that is 21″ inches deep it won’t make a great difference as the LED’s output will suffice either way with a little adjustment in the intensity.

This particular model comes with the basic 60º lenses, meaning the beams would provide a 60-degree angle of coverage. The spread of the light also depends on how far the fixtures are from the surface of the water. For my 125 gallons, I kept them at around 12″ off the water, with 85% of my lenses removed. The ones I left on were on my middle piece, though I had some pretty comfy looking SPS corals hanging out under the outer units. All looked gorgeous, thrived and the growth rate and colors were more than satisfactory.

The right setup of lenses and mounting height is pretty intuitive, don’t stress it. Just monitor how your plants or corals react, that’s all.

To be fair, the only reason I now have 4 hanged on my 125 gallons is that I have a fairly obsessive personality. But in all honesty, I had no issues with only 3 units, and I was able to (effectively) grow just about anything under them.

Controllability

Being able to avoid light shock when introducing new species into the tank is something I value quite a lot.

LED lights give you the opportunity to control intensity down to the single percentage. You can also control both white and blue light to adjust your preferences on how you want to compliment your fish and plant’ colors. In a 125 gallon Reef tank, it’s a really helpful feature as you do not need to constantly move around corals to catch that elusive PAR reading.

Note: Just remember that PAR readings on LED lights are not at all the same as PAR with bulbs or metal halides. With LEDs you’d need way less PAR for your plants, so start slow and over the course of weeks test, test, test! Scaling with 3% to 5% intensity per week will be gradual enough to avoid bleaching.

A timer

A timer might seem less important but, it is, in my opinion, saving you a ton of anxiety. A reliable timer will take care of your plants for you, so to speak.

If you decide to run a couple of units the timers should be (obviously) synched. Some models of aquarium lighting can have very unreliable timers that go out of sync pretty quickly, which kind of defeats the purpose. From what I’ve tried so far, there were a couple of incidents like that. It’s frankly sad because the lighting worked properly, but thanks to inconsistent time frames my plants were suffering. I will mention the brands below.

Picking a brand according to your planned tank setup?

Below I’m discussing what model of light will best suit your setup. If you’d like to read more in-depth reviews of the fixtures mentioned below, you can check my full guide on aquarium lighting. Naturally, I’ve only selected LED lights as best options:


1) 125-gallon Reef tank:

For saltwater hobbyists light should only be seriously considered if they plan on growing coral. Live rock and fish are not pretentious about light so, a basic model on a budget would be more than enough for a FOWLR tank. For a 125-gallon reef tank, however, things will be different.

As we all know soft and hard corals need different lighting in terms of intensity. By the way, I think this is the part where I casually mention that the watt per gallon rule is too outdated to be considered as a factor. For example, nowadays LEDs can give off plenty of Lumens more per watt than a T5.

Lumen: a unit that accurately measures the quantity of light coming from a light source.

For an SPS dominant 125 gal tank with a depth of 21 inches, I can wholeheartedly recommend the 165W MarsAqua fixtures (visit the Amazon link to see some photos). They are the perfect budget-reef light and are worth every penny from what I’ve seen.

It should be noted that I haven’t done a head-to-head test to all available equipment or anything. It’s just that after some research I ended up buying these lights anyway, and they just kept proving themselves to me.

It may seem like a bold statement, but you can grow pretty much anything under them and 3 units seem to provide coverage for the whole 72 inches. My corals seem to agree as well. Try to keep the ratio of 1:3 white to blue light for a happy reef. It’s what has worked for me, but you can experiment.

By the way, I do have LPS too. Gotta love placing the occasional Anchor coral here and there.

On this note, the VIPERSPECTRA 165W comes at about the same price with a built-in timer feature. However, I did read in the reviews that plenty of people complain about the timers not being able to stay in sync. Back then I was thinking that having to look for a separate timer would be too much of a nuisance to go through. Well, I had to find out the hard way. Do listen to what actual buyers are saying. The timers were unable to stay in sync 3 months after my purchase, though the difference was just a couple of minutes. I would recommend this setup for an aquarium of this length, if you’re okay with occasionally checking the sync.

Now, if you’re on a tighter budget and want to go under a total of $300 then Amazon has a really cool solution – the Aquatic Life LED Aquarium Light. They don’t allow intensity control and lean towards the daylight rather than blue light, so they will be a good fit for a FOWRL as they will complement the colors of your fish. If this is the case for you, buy 2 fixtures of 36″ of the latter.

2) 125-gallon Planted tank:

If you want to read an in-depth guide on lighting an aquarium with plants that grow you can click here. In that post, you’ll see the science behind my recommended choices. Anyway, choosing the best LED lights for 125 gallon planted aquarium can be determined by which main category it falls under:

  • Lightly planted tank

    Before I turned my freshwater 125 gals into a mini-jungle, I started off normal – some driftwood, rock work, and a few plants here and there. I gradually added more and more plants and was really fulfilled by how they grew, occupying the whole tank eventually. Back then – starting on a budget – I had to do some overwhelmingly deep reading on the lights I could get that would fit my plants need as well as my wallet.

    Fast-forward a whole year after my purchase of choice and I was still using this – Amazon.com link for you. It has thousands of positive reviews right now.

    Coming at under $60 per unit, I was able to mount 2 of these over my 125-gallon aquarium (I got 1 x 46″ + 1 x 20″ for as little as $95 total). My observations – really good value for the money, not really bright, but more than enough for low light requiring plants, with a couple of medium ones in-between. I’m also guessing that many of you plan on having cichlids or Oscars in a fish tank of these dimensions. All I can say is that this light is quite literally perfect for such a setup as it brings out nice colors off of your fish.

  • Heavily planted 125-gallon tank

    When talking about a heavily planted forest-like tank we can’t go around scaling things up a little. Now, I hope I don’t get lynched for saying this, but I’ve found the Current USA Satelite Plus PRO (click on the link to check them out on Amazon) can really be something as LED lighting for 125 gallon planted aquarium setups.

    It gives enormous amounts of light and manages to feed all of my many many plants that sweet photosynthesis. Wait, photosynthesis is a process, not food. Whatever. For a 125-heavily-planted tank 2, 34.8-inch units would provide enough coverage. If you do the math you’ll see that getting 3 22.8 inch fixtures will waste you around 120 bucks compared to getting 2 34.8 inch ones for pretty much the same coverage. By getting 2 fixtures of 36″ – 48″ I made sure that there will be no shadowing as they are 34.8 inches long each, leaving almost no gaps between fixtures.

    Now, this lighting system does fall a little over on the pricey side, but it is well worth it, and I highly doubt anyone would want to compromise with their underwater garden. It has a ton of built-in features such as stormy weather, cloudy sky, moon and dusk and even a built-in timer.

    These lights easily handle my medium to high light requiring plants and the growth and colors really speak for themselves. To be honest, I did expect less, given how expensive lighting can get but the results I am having with my *ahem* HEAVILY planted tank really proved me wrong, thankfully. I think it’s safe to say this light is a top performer for the price range when it comes to healthy, thriving plants.

  • “High-Tech” tank

    High-tech aquariums require lots of strong, quality light among other sophisticated plant support. I am openly admitting that I never ran one of those things, so take what I’m saying with a grain of salt. Then again, I would not really recommend something that I don’t believe in. And by “believe” I mean researched, had similar equipment and, of course, discussed it with a couple of my trusted friends that do, in fact, own it.

    So, based on all of these, my friends and I came to the conclusion that the Fluval Plant 3.0 (also known as Fluval Plant Spectrum LED) is just about as good as it gets for a reasonable price. It’s a really powerful set of LEDs that was basically designed for high-tech planted tanks. As expected, it has multiple lighting modes, simulating anything from dusk to down. It also comes with 120º lenses, eliminating any beam light effect (again, perfect for plants that require lots of light). Another option here would be the Finnex Planted+ 24/7 CC. This product pretty much shares the #1 place with the Fluval as they’re both crafted with a single purpose – illuminating highly demanding planted tanks. The Finnex comes with a well-researched background, which you can tell by the way aquatic plants THRIVE under it. The scientific approach of the Finnex manufacturers allowed them to implement just the right wavelength (distribution of the portions of blue, red, green and white light) for an optimal plant growth. Note that this is more important than the PAR output. Anyway, both of these lighting recommendations will get your high-tech where you want it to be.

    There are 24″, 36″, 48″ sized fixtures from both, so for a 125-gallon tank you should get two of the 36-inch ones, as with the current pricing this setup will save you some $$$! The units can be extended, but this only gives flexibility in positioning, you will still be left with gaps if you get the smaller fixtures.

    A little disclaimer on the Fluval: This new 3.0 version gives off a little less PAR than it’s 2.0 cousin. That being said, it’s the newer model for a reason. LED manufacturers become better at employing more PUR (Photosynthesis Usable Radiation) per PAR. This means that the spectrum output is being continuously improved to match your pants’ needs. You can learn more about PAR and PUR in my full guide, which I linked to a couple of paragraphs earlier.

Honorable mentions

Okay, but what if your budget was a little looser? There are high-end quality lights out there that have impressive stats and features, no doubt. If you’re the kind of hobbyist who has a little more to spare (I’m looking at you, reefers) what would be a good reputable brand that has the right size to fit your 125 gal fish tank?

Many old-school aquarists would just worship the “BML lights” when a planted tank was in question. BML used to be a brand that would manufacture aquarium-suitable lights which were as efficient as they were pricey. However, they decided to rebrand, specializing in horticulture lights, dropping off the aquarium alternatives. They are now known as Fluence Bioengineering. Still, many advocate using their non-aquarium lights for fully planted tanks. I have not tried their new products, but as far as I know, aquarium suitable lights do come off as more durable while exposed to evaporations with some being fully water-proof. They do make 72″ fixtures, specially designed for plant care, so there’s that. I would recommend.

Another brand, I think deserves mentioning is Kessil. They have some pretty neat fixtures, with a lot of specific controls which combined with their output potential, is earning the unconditional love of the more advanced aquarists. Though you can’t go wrong with Kessil and their high PAR LED aquarium light solutions, If you want to cover your 125-gallon tank with these, be prepared to leave at least $700 on the table.

Conclusion & final words

Size matters, but so does your plan and setup. Properly lighting up an aquarium that is 72″ long is more of a special case, but not impossible to overcome. If you need further guidance on your 125 gal fish tank, just leave me a comment and I will happy to reply as soon as I approve it. Speaking of which, it makes me really happy that more and more people are leaning towards the bigger tank. Having one of those can be a great delight. There’s nothing that can compare to growing your own pants or a reef colony in a huge aquarium.

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aquadminzacRob MDirk De BakkerMike Rawlings Recent comment authors

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Mike Rawlings
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Mike Rawlings

Hiya, Firstly.. thank you for writing up these articles. Ive learned more in the last hour than i did in the previous 5!! So much conflicting info on the web. Ive got a 90 x 26 x 30 inches (deep) aquarium arriving. Ill be happy to grow low light plants anubis / crypts / moss etc but am struggling to find a light solution. In the uk ive yet to be able to find the finnex ray 2 for sale. Aquarium will have a hood and so i’ll need to fit the lights within it. If i went with 4… Read more »

Dirk De Bakker
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Dirk De Bakker

Hello, really interesting articles so much valuable detail. Are the lighting units powered by transformers or direct AC supply. We use 240v in Australia and wondering if this is a problem. I am setting up a 60″X 24″ X 24″ and thinking of 2 units to get full length coverage but reading on your lens manipulation that might be another less expensive option. What would you suggest. Tank will be heavy plant and light on fish numbers. .
Thanks for your time and the articles are great.
Regards, Dirk

Rob M
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Rob M

I have a 125 gallon planted aquarium that needs help. I would be very content with basic/low light/ low maintenance plants but would like your opinion as to what lighting to use. I have two 36 inch compact fluorescent fixtures but one of my bulbs just burned out. I purchased inexpensive 6,000-6,500 full spectrum bulbs but am ready for an upgrade now. One of my problems was my water softener using standard salt. I didn’t have problems with my African Cichlids but with tropicals and live plants that is a different story. I have stopped using my water softener to… Read more »

zac
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zac

Thank you for the article.

I have a 125 Gallon Aquarium and I’m trying to grow Anubias. I’m trying to reach 1-2 Watts per gallon.

Two 36″ Satellite lights would be 50 Watts of light only totaling 0.4 watts per gallon which is far from the recommended 1-2 Watts per gallon.

Am I doing my math wrong or perhaps going about this in an entirely incorrect way?

Thank you.