well there are small species of pistol shrimp, and cleaners can get sorta large. Ive had 2 cleaners and a pistol in the same 20 gallon tank for about... 6 months now, they havent even met each other yet since the pistol spends all day and night in his cave. Pistol is about an inch, the cleaners are about 1 3/4ths of an inch.