Last spring i added eighteen cleaner clams to my 285g fish only tank. At first they all buried themselves. But over the course of two weeks the shells of two of them showed up. About two monthes ago i added more rocks and dug up fourteen clams. Figured that wasnt so bad. Recently, after the addition of a chocolate chip star they started to die off. Im not sure if the star is digging them up and eating them or if they just died and got eaten but i figure i still have about ten left. My sand bed is four inches at the shallowest part. Never added any filter foods so how they lived so long i couldnt say. Just my experience