Franna, if your tank temp reached 30 degrees this could have been a cause for the fish gaping. The amount of dissolved oxygen ( solubility of oxygen) is reduced as the temperature increases, so you need to find a solution to bringing the temp down in any event. The corals in your tank are slightly forgiving of temp's above 28 deg C, but will not tolerate this on a continual basis.
If you cannot invest in a chiller or find some other mechanical method of covering the tank etc., my advise would be to ensure agitation of the water surface to speed up evaporation. The evaporation will help cool the tank volume slightly.