Rays swim the sides of the tank.
That is heater burn and now looks like "death curl".
If you ever try another ray you must cover the heaters and/or incorporate a sump to keep the heaters in.
It is easy to think "heaters are not that hot...they are in water". If you ever touch one when they turn on in that water you will think different. Rays do not have scales to protect them from getting burns.
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