Tank lid? Good or bad?
 

I have tried hunting for info, but I am coming up pretty empty handed. Any opinions or links would be appreciated.

Is it better to have glass tank lid on the tank or not? I know our freshwater tanks are hit hard by evaporation and heat loss when we remove the lids.

Some people have eggcrate to allow light and block flying fish. Wouldn't that melt under the lighting? Doesn't eggcrate block some light anyways?

I am by no means an expert but my take on it is yes egg crate blocks some light but it is minimal and you have to wiegh this with the danger of flying fish. As for evaporative loss my understanding is as long as you top off consistantly it can actually work for you by helping with cooling your tank .
Most of the tanks I have seen are topless and this must be for a reason.

I made a mesh top for my tank. Doesn't trap any heat, blocks very little light if any and I haven't had any carpet surfers.

Leave the lid OFF and get an auto-topoff system.

The tank cools itself through evaporation. Leaving the top on also prevents proper gas exchange which will drive down pH in the tank because excess CO2 cannot escape.