Reef tank cover (plastic top)

[skiergd011013]

Is it ok to partially cover my 30 gallon reef with a plastic top? It doesnt cover it completely, theres still some open for gas exchange. Will it block too much light? It literally cuts the evaporation in half. This time of year i have issues with my windows getting a ton of condensation. The tank is in a bedroom. During the day i leave the door open for better ventilation.

 

[tdileo]

I have a plexiglass lid my dad and I cut and it covers like 80% and the rest is egg crated. The waterfall going into my sump, my powerheads facing slightly upwards and a refugium. Even my sump is about 75% covered and I don’t have any issues with pH swings or fish struggling to breathe.