There is a pleco. He will be gone shortly. I've never seen anyone mess with this guy. The tank he is in is fairly peaceful, but the pleco will go to a new home.
it can't be from a heater because they are in the sump. Thanks for the help guys. I'll do an extra couple of water changes this week
for two it seems that the pleco would have to keep rasping at the area for quite some time, and of coarse the stingray would move away in defense before it got to that.
I agree, it's a boo boo. Is there anything sharp in the tank that could have done it? Just make sure that you don't see any fungusing and keep the water conditions clean and it will heal fine.