12-27-2010, 06:16 PM
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I would not consider cabomba to be low light, nor hornwort. And if you are serious in saying "little to no light", nothing will grow with no light so there is a definite limit.
Ceratopteris (water sprite) floating should be fine, as it is close to the light source. But understand it will obviously shade the aquarium and less light will get through. I have grown fine swords under a canopy of water sprite, but not stem plants which generally require more direct light. If you can provide the tank size and existing light (type, watts, Kelvin, number) I may have more on the light.
The CO2 will not be an issue, if your swords are doing well now. I assume you are using liquid fertilizer? As someone mentioned, this is essential.