IMO, 10% WC 2x a week is too little. I always do 50% 2x week (same as you wednesday and sunday). When the weather is hot in So Cal, my water temp can go up to 88 degrees and my fishes are fine. just make sure there is alot of oxygen in the tank and you will be fine.
Just make sure you dont put it on full blast when refilling the tank to avoid any shock in drastic temp changes.