The glass lid definitely wasn't helping, most people use net tops to keep fish from jumping plus it doesn't block light when it's dirty and allows for proper gas exchange. The lights and motors in your pumps also add heat to the tank. If it doesn't cool off with the water surface exposed it's likely you will need a chiller. If the hot weather isn't common where you live you could always float some small bags of ice in the water to help cool it. Just be careful not to change the temp too quickly, livestock can handle warmer temperatures, even though the heat does reduce oxygen in the water, but they won't be able to tolerate rapid changes in temp