I may try some duckweed and floating anacharis, then! My worry about duckweed was that the fish would just eat all of it before it could cover the tank. Any advice on stopping it from getting caught in the filter intake? I heard that was a common problem with duckweed. Also how low is a low dose of excel considered? I know it must be a simple question but I have zero experience with ferts or anything of that kind!