the cons of a glass cover out weigh the pros, most reefers prefer open top it is better for the release of CO2 and the intake of O2 it also allows the tank to exhaust built up heat when Co2 builds up in your water column your PH will drop leading to your water becoming more acidic aquarium fish can live at 85 to 90 degrees fareinheit infact their natural habitats are this warm the reason you want to keep temperatures lower in the 70 to 75 range is to keep their metabolism lower thus decreasing the need to feed as often. you said you are new to this hence the big write up good luck and Welcome to canreef
