Room temp is fine for the cool end. Mine have a 83-84 hot spot. You shouldn't have to worry about humidity. Maybe mist a little bit when they are in shed. Mine are at 50%. A 20 gallon long is big enough for an adult. People use 32 quart or even 28 quart tubs. I use 41 quart. And is there a chance they were overfeeding it? It looks a little too plump. But I'm not experienced enough to say. Hope this helps!