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How Much Light For 125 Planted Tank

1659 Views 8 Replies 5 Participants Last post by  BryceM
I have a 125 gallon planted tank (18x72x24) that has been lit with two 182 watt T8 light systems. These systems are over 10 years old and they are falling apart. The bulbs fail regularly and I am continually replacing them. The hardware itself is also deteriorating. I am looking at a Tek Light T5 Fluorescent Aquarium Light 4ft 6 bulb 324W system. Is this sufficient or do I need to order an 8 bulb system. These are quite expensive so I want to make certain I am ordering what I need. I would appreciate any help.
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It really depends on what type of plants you want to grow. Most hight light plants will live a 3wpg and will thrive a 4wpg. I would recommend co2 if you go over 2wpg, and stay away from 5wpg unless you have a lot of experience with hight light tanks.
I have the 6 lamp t5ho 324 watt over my 90 gallon. So for a 125 i would go big with the 8 lamp. If your looking to save you could get the retro kit from tek light but regardless go with tek light, their great!
With high-quality T5 fixtures and a 125g tank, I think you'd be fine with 2wpg for most plants. If you're going for outstanding color and the ability to grow any species out there, 3 wpg of T5 would be more than plenty.

Keep in mind that going from T8 to T5 fixtures will result in a 200% to 400% increase in efficiency per watt. You'll probably need to adjust ferts, trimming schedules, and of course, CO2 has to be absolutely optimum at high light levels.
I appreciate the quick and very helpful responses. I am concerned, however, that with the introduction of high light I may have to supplement CO2. I have done so in the past but have found that with the more common plants, i.e. Java Fern, Amazon Swords, Valisneria, Myrophyllium, and etc. that the plant growth I achieve with lighting alone is more than adequate for my tastes. Then again, I have never used High Light and do not know what to expect.
Really high light is a very different world. Go for it, but don't expect to get away without making any other chagnes. Stay on top of your ferts and CO2 and you should be fine.

One thing you might want to consider is a fixture that gives you flexibility to run only a part of the lights at any given time. This will increase your flexibility if you want to adjust as time goes on.
I have elected to buy the Tek T5 4 foot 6 bulb system but now have to make a choice of bulbs. They offer mixes in 6K midday and aqua blue as well as aqua blue plus, actinic, pure actinic. Does anyone have any suggestions which of these bulb combinations I should order? Thanks for all of your help.
Unless you want one simply for aesthetic use, you don't want the actinic bulbs (they're designed for SW corals, though they will bring out neons and blues in fish...)

The 6k bulb is one of the best for FW plants.
I'd stay away from the actinics. Like Lauralee said, they're designed for corals.

My absolute favorite T5 bulbs would be a combination of 10,000k bulbs supplemented with a couple of AquaMedic Planta bulbs. The Planta bulbs have a bit of a pink color to them and they really bring out the reds and greens nicely. It makes the fish look better too.

Many people are in love with the 9,325K Geisman bulbs. Don't just accept the bulbs that come with the fixture. The right selection makes a large difference. Whoever is selling you the thing may give you a discount if you decide to get your bulbs from another source.
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