There are chillers available (saltwater tanks sometimes use them), but they cost about $500 and up.
Do you have air conditioning? That can keep the temps down, but of course it is expensive to run. What are you room temperatures like? If the lights are making the water hot, you could install a fan under the hood (if there is room), or point a small fan at the tank to take away some of the heat.
Many people float frozen plastic soda (Pepsi etc.) bottles filled with frozen water in their tanks to keeps temps down. Of course, that could be a pain to do every day in summer, but it certainly is a cheap alternative.