Can you run your lights too low? - The Planted Tank Forum
 
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post #1 of 7 (permalink) Old 01-17-2011, 02:40 PM Thread Starter
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Can you run your lights too low?

I have a 210 gallon system running T5HO's and have had a running battle with black brush algea. I was trying to run my system really low tech (no co2, tank uses a sump) to help keep the maintenance down. The lighting consists of 4 rows of bulbs running the entire length of the system, i had it so one pair of tubes would be on at one time with a overlap of about 30 minutes in the middle of the day.

I decided to try a experiment this weekend and kicked on both banks of light full bore all day long, each day after about 2 hours I actually started to notice pearling off of my vals! My anacharis and wisteria both grew much faster and I noticed no increase at all in algae growth.

I am going to run this same setup all week now to see if the results continue to pan out, my question is this. Has anyone ever found they were running their lights to low to discourage algea growth but instead ended up retarding plant growth and giving the algea a better chance to grow?


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post #2 of 7 (permalink) Old 01-17-2011, 03:24 PM
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i did the exact same with my low tech tank, once i added more light the amount of algae went way down and my plants grew out like crazy. Its that increase in plant growth that decreases the algae. when the plants are growing at their optimum, they use up all the nitrates leave no nutrients for the algae to grow. I would run it like you said for a week and see how it goes.
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post #3 of 7 (permalink) Old 01-17-2011, 03:31 PM
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well there are a lot of factors. Yes you can run lights too low, that's why some people question the ability of the early LED lights for plant growth, as they don't put out enough light. For a newer tank especially with enriched substrate like you have there will be a good amount of nutrients for the plants to go off of initially. But as you increase the light your plants grow faster and start using up those nutrients and once the are low on nutrients and slow down their growth, algae will start growing.

I may not be 100% correct, but I am speaking from experience with a 30g x-high tank (24" tall) that had two 15W tubes and two 13w CFL spirals in a diy hood no reflectors, one would think this setup to be low tech/light level, i ran all the lights 12 hours a day, had beautiful growth but after 6 month or so the growth slowed and I began to get BBA, i have since cut off the two CFL's all together and cut down on the photo period of the tubes.

My advise is go ahead and experiment, you will probably want to be adding ferts, if you are not already. But at the first sign of algae cut back. BBA is a pain to get rid of in low tech non CO2 setups, definitely don't want it if you can avoid it.
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post #4 of 7 (permalink) Old 01-17-2011, 06:52 PM
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Originally Posted by BonesCJ View Post
Has anyone ever found they were running their lights to low to discourage algea growth but instead ended up retarding plant growth and giving the algea a better chance to grow?
I have, but not because I was trying to solve an algae problem. I simply though my lights were adequate when they were in fact marginal.

The interesting thing during this time is that I found reducing (but not eliminating) phosphorus dosage greatly reduced algae, with almost no effect on the plants. That's at odds with conventional wisdom, and led me down the wrong path for a while. Looking back on it now, the only explanation I've found is that I must have been forcing the plants to consume alternate phosphorus sources, in particular organic wastes that may have a specific role in promoting algae growth.

Of course, increasing lighting both improved plant growth and eliminated the algae. It seems the plants were then growing fast enough to naturally control organic waste levels, without having to manipulate them into doing so by limitation.

It's also not the first time I've seen phosphorus have unexpected effects on algae. I've created some spectacular multi-algae blooms in the past by adding phosphoric acid (used as a pH reducer), whereas it's been proven that adding huge amounts of potassium phosphate doesn't have the same effect.

All this leads me to believe that algae prefers specific forms of nutrients. When all is well, plants out-compete algae for those specific forms, even though the total amount of that nutrient present and utilizable by the plants may be effectively unlimited. Too little light and plants can no longer do this.
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post #5 of 7 (permalink) Old 01-18-2011, 02:32 PM Thread Starter
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I have, but not because I was trying to solve an algae problem. I simply though my lights were adequate when they were in fact marginal.
I have wondered that myself, my tank is 7 * 2 * 2 and I run 362 watts of light, running the numbers at full blast thats only 1.8 wpg. I know that is not the end all of numbers but even then it seems like it might have been really low light to have only been running HALF those lights at any one time.


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post #6 of 7 (permalink) Old 01-18-2011, 04:36 PM
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i did the exact same with my low tech tank, once i added more light the amount of algae went way down and my plants grew out like crazy. Its that increase in plant growth that decreases the algae. when the plants are growing at their optimum, they use up all the nitrates leave no nutrients for the algae to grow. I would run it like you said for a week and see how it goes.
It isn't possible for plants to use up all of any of the nutrients and thus starve the algae. Algae require almost no nutrients, compared to plants. All tank water contains plenty of nutrients for algae, no matter how well the plants are growing.

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post #7 of 7 (permalink) Old 01-18-2011, 04:40 PM
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I have wondered that myself, my tank is 7 * 2 * 2 and I run 362 watts of light, running the numbers at full blast thats only 1.8 wpg. I know that is not the end all of numbers but even then it seems like it might have been really low light to have only been running HALF those lights at any one time.
Watts aren't a measure of light, so 362 watts is just the amount of electricity the lights take to light up. You have to evaluate lighting by what type of light it is, T5NO, T5HO, T8, PC, what quality of reflectors you have, and how far the substrate is from the lights.

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