java ferns like low tech low light tanks. The most beautiful, greenest, biggest, lushest java fern I have ever seen is in a neglected 20 gallon at school. It has a 5 watt flourescent, no water changes, no ferts. It literally takes up the entire tank with huge daughter plants on the end of every leaf, I thought it was a giant silk plant at first. In my high tech, hi light, EI Ferted tank my java ferns look OK but not great, they need alot of potassium and phosphorous to look good with high light. I put them in my low tech betta 10 gallon with a 15 watt T8, no ferts, they green right up and start growing faster.