I bought a mystery snail tonight and plopped it in Fishie's tank. It was slowly coming out of its shell, and within about 15 minutes, Fishie discovered there was another living thing in his tank and he attacked it. The snail retreated into its shell and rolled on top so that its opening was concealed. But then a few minutes later it started coming out of its shell again and Fishie nipped at it again until it retreated back into its shell. It hasn't come out again since, but Fishie keeps swimming up to it and flaring. Should I remove the snail or does Fishie just have to get used to the fact that snail is there?