I need a filter for a tank of baby trapdoor snails BUT HOB filters won't work as they will not fit over the rim of the storage bin. It's about 10-15 gallons of water but I'm thinking of getting maybe one for 30-40 gallons.
I though maybe sponge but do they only do biological filtration? I need something that will do mechanical and chemical as well. The water gets a nasty smell after a day or two. Maybe I need a bigger tub but there are only 15 small snails in it and according to aquavisor its not over stocked.