filter media

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...

I'm contemplating building a narrow internal sump along the back wall of my long 20 gal freshwater aquarium (12x12x30). Because of where I live and the set up I have here, I can't set up an external sump, but I'd like to get something better than the pop bottle filled with ceramic pellets...