Temperature control

[Painterroy]

I have a new 5 gallon hex tank which I'm cycling before i add fish. I have plants in there so I am running the light on it for about 8 hours a day to keep the plants healthy. But I find running the lights raises the temperature to about 81-82 degrees. Obviously I don't even run the heater right now (maybe in the winter I won't have this problem). My question is how to get it down to 78 degrees with the lights on. Can I take some water out and replace it with new water (dechlorinated) but colder to take the temprature down?

 

[aqua_chem]

What kind of light is this?

 

[Painterroy]

It's just a small compact florescent that comes with the Marineland 5 gallon hex tank