I have this white gunk on the tip of my aquarium heater. It's only on the black plastic part at the bottom, not on the glass part. The tank is definitley cycled now, so I thought it was just part of the good bacteria that's supposed to be in the tank. I saw the guppies eating it last night, and now I'm kind of worried. Is it Ok for them to eat? I've been careful not to overfeed now so there's no food in the tank leftover, but the fish always seem to be looking for food. I have two guppies and five cory catfish. Only the guppies were eating it. Thanks!