The stuff that he sold you that gets hot is probably cal-hypo which would explain the calcium hardness reading. I wouldn't use it anymore in your pool. By the way, if your CYA is 50, you only need to take the chlorine up to 15ppm when you shock. (Take a look at the Best Guess chart in my signature below.)

Are you certain of the volume? 25K would be a pretty big AG pool. What size is it?

Welcome to the forum!