ive a kuhlI loach who likes to lIve in the external filter. he has been living there now for for 4 months. every time I clean out the filter he's there, so I gently transport him back to the tank. as soon as I do this he's back in the filter. he's obviously finding food in the filter and likes his own company ;D there is not much I can do about it because he swims up the pipe that throws out the water that has been cleaned in the filter. ' must be a good swimmer because the water comes out of the pipe at some force' so I guess all I can do is let him get on with it.