i have a tank that was used for my fry as they grew i moved them to a 55 gallon tank and stored the 20 gallon.i left the gravel in it and cover it and placed it in my basement.i was gonna set it back up but realized my girlfriends cat decided to use it as her littler box.is there a type of cleaner that wont leave behind any residue or should i just throw it out?
