Hello there!

You can get higher wattage heat mats if need be, but in this case a low wattage 25-30w spotlight mounted outside the tank aimed at a branch giving a hotspot of 28-30C might be an idea they shouldn't suffer an adverse reaction to a drop back down to 24-25C on a night so you could put the spotlight on a timer!


Also you don't say if you have any other sort of lighting in/on the tank?


Steve