Egg crate is the grating used on flourescent lighting in dropped cielings. It has squares about 3/8" and is plastic. You can get it Home Depot. Set it on the tank top. Youll get the light through and the gas exchange but not the fish.
The glass top is the problem. Fans and romoving it will do the trick!
I use a fan blowing over my tank and it worked great. I dont have any jumpers so I just leave the feeding hood open. If you are worried about jumpers maybe you could put window screen over the tank under the lighting?
I had egg crate on my tank. It took all of about 6 hours before my new diamond watchman goby went carpet surfing. I don't know if he went through the egg crate or if he just hit it hard enough and at the right angle that he was able to knock it high enough to get between the tank and the egg crate. So now, I keep my glass lid on the main tank, but use the sump to cool the water.
i totlaly love using egg crate, cheap and you can snip it to fit around anything you want..cut a section so you can remove it to get in to thetank when you need to.. the covered bread ties make for great locks too..
for the 125 look in the paper sometime you will find great deals on them!