I think there is something other fish carry in that they are carriers but not effected. only the cories. Because if you are Deep cleaning and keep the Substrate clean. I could not keep cories, Pandas specifically. I discovered one pet store must have been hidden danger lurking under the surface of the fish. Every time I added a new fish, i'd lose a cory. I stopped going to that store for months. Then got my cories from another store. I didn't add anything but Dipped decontaminated plants. I still have one little cory from that group. Try another store, and clean the heck out of the sand. Might I suggest some Malaysian trumpets snails? They seem to eat junk under my sand too. plus algae! Now its a paradise. i have a trio of pandas, 1 albino, 1 pepper, bunch of rescues. Try a different species!