04-15-2009, 11:15 AM
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The previous posts have contained much good information. I only want to follow-up on Mikaila31's thought about too much light.
From my research I would conclude that the limiting factor for plant growth in a planted aquarium should be the light, as opposed to nutrients or CO2. Too little light and plants will fail to thrive and grow, too much and the plants will use all the available CO2 and algae will flourish because it is better able than plants to get carbon from bicarbonate. Without CO2 addition, no more than 2 watts of full spectrum light should be over a tank. As noted preivously by others, this can be calculated for the newer type of compact bulbs.
Like Mikaila31, I strive to get the "colour" that I prefer, using a mix of flourescent tubes (2 over each tank) but all full spectrum or versions of full spectrum. The cast of my 90g is slightly different from my 70g because of the second tube (one is always straight full spectrum). I have about 1w per gallon (80w over each tank), on for 13 hours each day, plus some daylight in the room. I do not add supplemental CO2. I use liquid fertilizer twice a week (leaves definitely start yellowing and becoming transparent if I only fertilize once a week--I've twice experimented with this in the last 6 months), and there is no algae to speak of. I've managed through good luck to strike the necessary balance between available CO2, nutrients and light. You can see how this looks in my aquarium photos.