If it ever did get too warm, you could fill water bottles with water and freeze then, and then let them float on top. I personally fill a ziploc baggie full of treated tap water and freeze that. Once it's frozen I drop it on the floor a couple times to break it up, and put the chunks in my tank. My water at room temp is probably 75F, and my axie tank has to stay below 68F, so it's a struggle. Having a fan propped up on a screen top works well for me. But some days it gets too warm and I add the ice.