Sand filter medium

So out of frustration because of the wife stressing out I took what I had and mixed it with 25ml of distilled water and tested it for CH. It tested at 50ppm. So I know it's calcium. So I guess trying to figure out why I have it is the question as my CH is usually around 310-340. I'm also struggling to maintain FC ever since the pool builder left my swg off for 2 days. So I've been slamming pool and have used 10+ gallons of chlorine so far and I still dropped from 18ppm at 9pm last night to 9ppm at 730am today. Frustrating because I can't seem to figure out why I'm losing FC still and why I keep getting this calcium all over the pool.
 
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