txdurk, we studied the different media and how they handled the Texas heat.. turns out, its not an issue.
they may heat up on the top, but dont transfer the heat much... just dont let your water get any closer than one inch bellow the surface and it should be fine. ...now how much heat are you reflecting onto the plant is another story.
FYI - i use granite and river rock,,, its served me well for four seasons... oh, and i havent had to adjust the ph for 3 years.
Randall: Fantastic. I can afford that and it fits. I'm thinking 30% should I order it. What do you think? I see your link was to 40%.