My betta tank is a 5 gallon with a sponge filter. There are plants (java fern just added, water sprite and a floatin glily pad plant) and 1 snail other than the betta. I have been having a problem with brown algae for quite awhile. I thought it was due to low light levels, so I bought a flourescent fixture with a regular bulb at 15 watts (3wpg). That didn't seem to help and recently I have been getting a green biofilm growing on the rocks and some plant leaves. The plants aren't doing great in this tank but do well in the other tanks. I just switched to a coralife bulb, I have been adding an iron rich fert all along and I have recently upped my water changes to twice a week with gravel vacuum. Any ideas what is going on in this tank that doesn't affect my other tanks. It can't be the water. Any other info needed?