What type of filtration do you have? Is your tank predrilled with overflows? I have 2 motoros with 3 tinfoil barbs, a gar, and a clown knife. The bottom of the tank is covered with about 1 inch of sand. The stingrays movements seems to kick up their poop and that gets sucked up in the overflows. I have a predrilled tank with 2 overflows with slots on the bottom, middle, and top. I never have to siphon or kick up the sand. It is pretty much always clean.