06-08-2013, 06:06 PM
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First, as you probably noticed, the special "plant bulbs" are not as bright as other bulbs. The FloraSun puts out way less photosynthetic radiation than the T5HO UltraSun. As you found out, T5HO is way too much for the shallow 20L tank. I would think the T8 would be plenty! I use two CFL bulbs on my 20L, it's covered with frogbit and duckweed, and my Swords, Cabomba, and other plants do very well, although they grow slowly.
Did you use "Daylight" bulbs or "soft white"? That can make a huge difference in the spectrum of light. I would expect a T8 Daylight bulb would be just what you needed. Perhaps it's not the light, but your plant selection (stems?) or some other parameter?