fluval 307

I have 3 tanks: * less than a gallon (2 plants, sand-like substrate, bladder snails to keep it clean, bio filtration only) * 3-gallon (a couple of male fancy guppies & a nerite snail, heavily planted, smooth pebble substrate, bio filtration only, moving to a 10-gallon) * 29-gallon tall (1 VERY...