My grouper has been rubbing himself on the sand and he has been eating quite well also he has this mark I thought at first was just his coloring it’s not identical to the other side hes hard to tell I was thinking the temperature because I have a glass lid heat gets trapped so it gets hot like today it was at 83 is that why the grouper is rubbing himself on the sand or no if so how do I cool down the tank also the grouper is a dark hind grouper