You could try root tabs. I have had two amazon swords for about 3 weeks now one is in a 5 gallon hex with 10 watts of CF light, the other in a 10 gallon with 20 watts of CF light. I only use a liquid fertilizer 2 drops a day, in the 10 gallon. Maybe one drop every other day in the 5 gallon. Trying to cut back on the drops, because of algae. I use tahitian moon sand, which is just like plain gravel with no nutrients. So far they look alright, and roots are growing like crazy. I hear they are tank busters, but I'll enjoy them for the time being. The only thing I am worried about is any possible deficiences that haven't shown themselves yet. But yeah there are little tabs that you can buy, especially for this type of plant that takes most of its nutrients from its roots.