[hllywd]

My tank gets some sun through the summer, and I try to keep the shades open to gain any benefit from it I can. The point of our high intensity lighting is to replicate sunlight, why keep the real thing out (unless heat is a problem)???

Sunlight isn't your problem. Find out what's causing your water quality issues and you won't need the shade. Do you do any regular water changes? That might be a start to improve the water quality. You may also try a media reactor with some GFO for phosphates, I've had some bubble algae issues and that seems to have helped tremendously. Nitrates and phosphates will build up over time and you need to export them somehow.
Tim