Heat

There are a couple of things to try.

If there are no live plants, leave the lights off as they generate heat.

Open the lid, or remove it if possible. Arrange a fan to blow across the water surface. The latent heat of vaporisation should reduce the water temp slightly. [The moving air will evaporate the water, and water uses energy to evaporate; it gets this energy from the heat of the water]

Fill some pop bottles almost full of water then freeze them. Float the frozen bottles one a time in the tank. When the ice has melted, put a new frozen bottle in the tank and put the melted one in the freezer to refreeze. Safer than adding ice directly to the tank as there is no danger of the tank overflowing.

the pop bottles sound a good idea , i did think of ice but wasnt sure about it .
i am a little nervous to live lid open when i am not in the house  but i do tend to leave it open when i am home 

And with the heat, you should be able to collect a few empty pop bottles fairly quickly 

even quicker if  beer was in bottles not cans 

Exactly! However; I draw the line at red wine in PLASTIC BOTTLES

i would draw the line at wine - cant stand the stuff