temperature suggestions

[silke]

since i keep many herps in a 1 bedroom apartment, the room temp is around 80
i'm having trouble keeping my 20 gallon fish tank temps down below 80 so i have to leave the flap on the lid open when the light is on since the light raises the temp too much
the temp is still too close to 80 ....

can anyone suggest what i can do to lower the temp. of the water?

thanks