[glass-gardens.com]

I was having the same problem as many with my tanks over heating in the summer temps, even with AC. At least for my part, the big problem was the tight fitting glass lids basically preventing any air circulation at the surface and I suppose having even some type pf green house effect.

I took the lids off for awhile, but I have japonicas in all my tanks so some kind of cover was needed. I ended up buying some white plastic "egg crate" diffuser panels, the kind you use in false ceiling flourescent fixtures, 2' X 4'.

The grids are about 5/16" thick, made of white rigid plastic with a grid of about 5/8". I just cut them to fit inside the rim and it's been working great with about a 4 degree drop in the temp peaks and no escapes, and in my 75, it's allowing me to experiment with the CFs I use by allowing placement to get the exact coverage I want, concentrating light on higher light plants and less on lower light plants, and least for now, I've seen a noticeable difference in plant growth and less algae.