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How high should i raise the light?

703 Views 7 Replies 4 Participants Last post by  Hoppy
I am sick of algae and the demands of the higher light setup right now. As you guys know from my other threads, i have algae problems. I have a 65 watt aqualight over my 20 gallon. I am going to be mounting the lights over the tank with a diy method of my own. How many inches should the lights be above the edge of the tank to achieve an intensity of about a 2 watt per gallon set-up. I want the light to be strong enough to grow various stems like sunset hygro, red ludwigia, bacopa, and plants like pennywort, aponogeton crispus, dwarf sags, and marsilea minuta. These are the plants I have so how many inches should i raise above the top edge of the tank?
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ok, well i couldn't wait and just went for an experiment. My light was only on the aqualight legs and about 2 inches above the top but now i made a diy light mount that has my 65 watt light 4 and 1/2 inches above the top. Hopefully the algae will reduce. and the diy i made looks better than the mounting legs in my opinion.
It depends on the height of your tank. 20 gallon tanks come in several different heights. To drop the light intensity in half (approximately) increase the distance from the substrate by a factor of 40%. So, if the light was 16 inches from the substrate, increase that to 22 inches. If you had high light intensity and want medium light intensity, that would do it.
Well it is a 20 gallon tall. I was having a problem with algae especially hair so i figured i would lower the lights first to reduce the demand for co2 and ferts to balance. the lights were about 1 and half inches before and now about 4 1/2 inches to 5 inches above the tank edge. So it was an increase of about 3 and half to 4 inches roughly. Do you think that should make a difference? Now should I reduce ferts now that the tank has lower light and the tank is lightly planted since i lost a lot to algae?

Let me know guys, thanks.
I added some high light loving floating plants to cut down on light penetration on my low tech 29 gal. I like the shaded look too. You might want to consider that.
So do you guys think at the new height i will be able to grow the plants mentioned in the first post. Is it going to effect the growth rate of my plants at all or will it be hardly noticeable?
You raised the light about 3-4 inches, so you reduced the intensity by about one third. I don't think that is enough to affect the plants, but also probably not enough to make your algae problems be less. The plants you mentioned will all grow with low light, as long as they also get good CO2. That suggests that you would help yourself more by raising the lights about another 3-4 inches.
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