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 fish tank dimensions, the right fixture size becomes the trickiest part.
Moreover, I know how keeping light-dependent livestock in such a big space can get complicated.
So which fixture classifies as the best lighting for a 125-gallon reef tank, for example?
What about planted freshwater fish tanks?
I think I can help.
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, for example.
But what else?
In general, this is 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 fit the tank accordingly (72″ x 18″ x 21″). The 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 lights have worked for me.
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
The first thing you need to decide on is the type of lights that your particular fish tank setup would need. Depending on the livestock and aquascape you want in your aquarium, different suitable light sources can be considered.
Generally, you can choose 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 eighths 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 the former is more compact and lasts for as much as 20% longer.
However, this may not be the case for a 125-gallon tank…
The main drawback of these lights 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 a bulb loses intensity. For a 125 gallon tank, it may get costly as you’ll either have plenty of bulbs to change or you’ll have serious difficulties finding the 72″ long tubes.
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 6-feet 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 aquarium plants and corals with high lighting requirements without spending a fortune on electricity bills.
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 halides is the shimmering effect they give off.
You know, the one that mimics the natural light in the ocean.
Anyway, a reef tank with metal halide lights is becoming less and less common.
A 125-gallon aquarium is a little over 20 inches deep and these rather expensive light bulbs may not fit your budget…
Disadvantages are not absent when it comes to metal halides.
Remember 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 with 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-tangible.
Despite being a popular choice among reef keepers I’ve found that under metal halides some of my corals do not show their full colors.
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, 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 the one a Metal Halide would provide.
LED lights 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.
Anyway, the color rendition with LED fixtures is a breeze.
It can be a gamechanger for reef aquariums and planted tanks alike.
Personally, I like my plants and corals to be as colorful as possible.
From what I’ve observed, after switching from MH to LED lighting 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 to my freshwater tanks too – there’s nothing like a beautifully complimented colorful fish.
Another thing I fancy about LED lights is that there is no need for an aquarium 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 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.
I included.
Now I know LED lights 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 aquarium lighting 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 longevity of LED lighting is the way the fixtures manage heat.
They have a special heat sink from where the heat leaves.
This results in the LED lighting having a lifespan that’s 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 illumination
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 rock and fish don’t care that much for specific lighting. Your only concern here would be what type of light will best complement your beautiful aquarium fish.
However, aquarium 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 tank, 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 aquarium.
By removing the lenses you will lose some intensity but get an even light spread.
LED lights 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 carried out by anyone.
If you haven’t done such a thing – don’t worry, it’s super simple. All you need is a screwdriver and 20 minutes from your time.
Here’s how it works:
- 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 the inside plate.
- Carefully unplug each diode.
And here’s a video of some guy doing it:
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-gallon tank, I kept the lights 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.
Correctly setting up lenses and mounting height is pretty intuitive, don’t stress it.
Just monitor how your 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 any coral 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 a single percentage.
You can also control the white, blue, red, and green light to adjust your preferences on how you want to compliment your fish and plants’ 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) synchronized.
Some models of aquarium lighting can have very unreliable timers that go out of sync pretty quickly, which kind of defeats the purpose.
Picking a brand of aquarium lighting 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 the best options:
1) 125-gallon Reef tank:
For saltwater hobbyists, aquarium lights should only be seriously considered if they plan on growing coral. Live rock and fish are not pretentious about the light so, a basic model on a budget like the Beamswork DA FSPEC Pent would be more than enough for a FOWLR saltwater aquarium (Fish Only With Live Rock).
For a 125-gallon reef tank, however, things will be very 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, LED lights can give off a lot more light intensity per Watt than a T5.
Anyway, for a 125-gallon tank with a standard depth of 21 inches, that houses SPS corals I can wholeheartedly recommend the 165W VIPARSPECTRA fixtures (visit the Amazon link to see some photos). These LED lights are the perfect budget option for a reef tank and are worth every penny from what I’ve seen.
It should be noted that I haven’t done a head-to-head test on all available budget 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 any aquarium coral under these LED lights and 3 units seem to provide coverage for the whole 72 inches of the tank.
The corals in my reef tanks seem to agree as well.
Try to keep the ratio of 1:3 white to blue light for a happy reef aquarium.
This ratio has worked for me, but you can experiment.
By the way, I do have LPS corals too. Gotta love placing the occasional Anchor coral here and there.
Anyhow, one disadvantage with the VIPARSPECTRA LED is that when dealing with multiple fixtures the timers tend to get out of sync.
The time difference is not much though – a couple of minutes for every 2 to 3 months.
I don’t mind dealing with that, and it’s a really insignificant inconvenience compared to what I get in return with my VIPARSPECTRA lights.
The Kessil A360X is another great LED fixture you can use for a 125 gallon reef tank.
It has a densely packed LED matrix that provides an excellent color blend and an equally amazing shimmer.
Which shouldn’t come as a surprise coming from the Chevy of aquarium lights.
With five of these babies, your corals and aquarium will come to life like never before.
When I started using the A360X in my 60-inch (152 cm) mixed coral tank, my softies and LPS immediately became more vibrant.
And the best thing about these lights is that they come with locked wavelengths so there’s not much you can mess up.
Unfortunately, you’ll have to pay a premium price if you want to experience all of the benefits they provide.
Anyway, if you want to see more options’, I recommend checking my guide on premium LED lights for coral growth. There, I review more high-end LED lighting fixtures that won’t leave you disappointed.
Visit the link and check out the premium suggestions I make for reef aquariums with a depth of 21 inches.
2) 125-gallon Planted tank:
If you want to read an in-depth guide on lighting an aquarium with plants that have explosive growth you can click here. There, you’ll see the science behind the choices I recommend below.
Anyway, choosing the best LED lights for a 125-gallon planted aquarium can be determined by which main category it falls under:
- Lightly planted tank:Before I turned my 125-gallon freshwater tank into a mini-jungle, I started off normal – I got some driftwood, rock work, and a few aquatic plants here and there. As a beginner, I was using mostly easy aquarium plants such as Java Fern and the like.
I gradually added more and more plants and was really fulfilled by how they grew, occupying the whole aquarium 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’ needs as well as my wallet.
Fast-forward a whole year after my purchase of choice and I was still using this. It has thousands of positive reviews.
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 – it provides really good value for its price, and even though it’s not really bright, it produces more than enough light for low maintenance aquatic plants. 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 aquarium 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 Satellite Plus PRO can really be something as LED lighting for 125-gallon planted aquarium (click this link to check them out on Amazon or click here to compare prices at Chewy).
It gives enormous amounts of light so it manages to meet the insane demands of my aquatic jungle.
For a 125-gallon, heavily planted tank, two 34.8-inch units would provide enough light coverage.
If you do the math you’ll see that getting three 22.8-inch fixtures will waste you around 120 bucks compared to getting two 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 the fixtures.
Here is probably the place to mention that a 125-gallon tank has a width of 18.5 inches.
If you plan on planting it back to front you may want to add secondary units to make up for the shadowing in the back and front bottom corners.
It will not be actual shadowing per se, but the plants at the parameter would get less light.
Note that you should only add parallel lighting fixtures if you want to cover the bottom of the tank with high-demand plants from back to front (which is rarely the case in practice).
Anyway, this aquarium 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 lighting simulations such as stormy weather, cloudy sky, moon and dusk, and even a built-in timer.
The Current USA LED lights easily handle my aquatic plants that require medium to high light, 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 its price range when it comes to healthy, thriving aquarium plants.
- “High-Tech” tank”:High-tech aquariums require a lot of strong, quality light among other sophisticated plant support.
I am openly admitting that I’ve only kept a couple of those systems.
This is more than most, but some will say that it may not be enough.
However, I am confident that my own personal experience, combined with the knowledge I gained during my research give credibility to my claims.
Therefore, I would not really recommend something that I don’t believe in.
And by “believe in” I mean I thoroughly researched, tested, or recommended by another fishkeeper with hands-on experience.
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 LED lights that were basically designed for high-tech planted tanks.
As expected, Fluval Plant Spectrum 3.0 has multiple lighting modes, simulating anything from dusk to dawn.
It also comes with 120º lenses, eliminating any beam light effect (again, perfect for plants that require lots of light).
The wide lenses eliminate the need for installing parallel units because this LED lighting fixture is really bright anyway.
Two 36″ to 48″ units will be enough to cover the whole length and width of your 125-gallon aquarium.
Anyhow, another option here would be the Finnex Planted+ 24/7. This product pretty much shares the #1 spot with the Fluval Plant 3.0 as they’re both crafted with the same purpose – illuminating demanding planted tanks.
The Finnex comes with a well-researched background, which clearly becomes evident when you see how 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 optimal plant growth.
Note that this is more important than the PAR output.
Also, know that the Finnex Planted+ 24/7 CRV version uses true Red LED diodes in the 660 nanometers wavelength range, which means that it will likely have the BEST impact on your aquarium plants. However, it is also the priciest from Finnex Planted+ Series.
Anyway, both of these lighting fixtures will get your high-tech aquarium where you want it to be. You’ll even be able to grow carpeting aquarium grass such as Dwarf Hairgrass.
Author’s note: Between the Finnex and the Fluval, I would personally choose the Fluval. Though they both grow fantastic aquarium plants, the Fluval has an IP67 waterproof rating. This means that water evaporation will not shorten its expected life. The Fluval also comes with a 3-Year Warranty, whereas the Finnex has a 6-month one.Anyhow, there are 24″, 36″, 48″ sized fixtures from both brands, 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 its 2.0 cousin.
This is the result of LED lighting manufacturers’ efforts to 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.
And finally, if you want a dedicated 72-inch long LED fixture for your 125-gallon tank I can recommend the tried and tested Beamswork DA FSPEC Pent Freshwater. This light is the brightest of the budget ones and has a decent spectrum to support aquarium plants.
For a heavily planted tank and carpeting plants, I recommend getting 2 72-inch fixtures and lining them next to each other.
Author’s note: Keep in mind that the 72-inch long Beamswork LED fixture may bow a little in the middle. That should not worry you, but no one would stop you if you find a way to give it additional support.
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, reef aquarium keepers) what would be a good reputable brand that has the right size to fit your 125-gallon 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 evaporation with some, like the Fluval Plant 3.0, being fully waterproof.
Anyway, Fluence does make 72″ fixtures, specially designed for plant care, so there’s that.
Another brand I think deserves mentioning is Kessil. They have some pretty neat LED aquarium lights (Amazon link), with a lot of specific controls which combined with their output potential, are earning the unconditional love of the more advanced reef 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 reef tank with these, be prepared to leave at least $700 on the table.
My Final Words
Size matters, but so do 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-gallon fish tank, just leave me a comment and I will be happy to reply.
Speaking of which, it makes me really happy that more and more people are leaning towards bigger tanks.
Having one of those can be a great delight.
There’s nothing that can compare to growing your own pants or a reef coral colony in a huge aquarium.
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Thanks so much for all your valuable information. I recently added a 125 gallon tank to my collection and just starting to think of how I will set it up. In reading your advice about using 2 Nicrew SkyLED Plus lighting fixtures for a lightly planted 125 gallon tank, I am not sure how you suggest for the fixtures to be placed on the tank. The 125 has 2 cross pieces at 24″ and 48″. How does the metal supports of the Nicrew lights fit on the tank so that they can be end to end? Do they need to be hung from above? or is there a way to place them end to end and still be level?
I currently have a Nicrew LED on my 75 gallon and trying to imagine how this will work. Thanks in advance. Jeff