lower the water level
open the top of the tank front and back
increase air circulation, point a fan at the tank
let water fall from the filter outlet
evaporation will cool the tank
shade from sunlight
raise the light fixture off the glass with some small supports to allow air to circulate
shorten light period
You might actually consider raising the heater setting to closer to the daytime temp of the tank if room temp falls a lot at night. If daytime temps are 80 and night time temps are 65, a small tank will go through big temp swings.
With hot lights you might go above room temp. Do what you can to get the tank to not exceed room temp, then set the heater to come on maybe 3 or 4 degrees below that maximum. As fall comes and room temp is not so high, you can lower the heater some.
