80 is really too warm for cresties especially young one. They like the temperatur to be in the 70's. The young one can get heat stress really easily. From my research they can be kept at room temperature all year round without problem. Cresties are so easy when it comes to housing them because they don't require supplemental heating unless you happened to live where it snow like crazy outside and the water start freezing like up north. If you are worried, try adding a 25 watt heat bulb. This way it won't get too warm.