I wasn't sure where to post this so I am going to post this here. I have a 55 african setup with crushed coral/marine sand mix as my substrate. I was cleaning out my xp2 filter when i noticed about 5 or 6 shells at th bottom of the canister box. The shells were twisted going from a small point at the bottom to quite a bit larger at the top at which point there appears to be an opening. Also the shells varied in size with one being smaller than a ladybug and the two largest being about a half inch in length. I dont believe they could have been sucked into the filter because of the strainer on the end of the intake and also it is "crushed" coral. Has anyone else experienced this or know what this is?