Hi, It sounds like you have brought something in that was immature and now has grown and living quite well in the tank. I'll bet it only comes out at night after the office traffic, vibrations from foot traffic and machines has stopped. Perhaps when the lights go out. I'd try setting a trap for the critter. Perhaps a tasty tidbit in a shrimp or minnow cage? Frank _______________________________________________ AGA-Member mailing list AGA-Member@thekrib.com http://lists.thekrib.com/mailman/listinfo/aga-member