Remove the glass cover. I thought I would never run my tank without a glass cover, but I was having temp problems, so I took it off and the temp dropped a degree or two. Since I wasn't sure that could really make a difference, I put the glass top back on and sure enough the temp went back up, that made me a believer. I still have to use a small fan pointed at the surface during the summer months. Just my opinion, that worked for my tank.