I have a bucket of hardness increased from Leslie's - which I am assuming is calcium chloride? On the tub it warns against premixing with water and especially not hot water as it says that beat will be released when adding this to water. With a brand new liner I am extra paranoid somewhat is the safest way to add the hardness up. I'll post another thread as I'm having trouble with the CH test but I believe right now I'm at 80 which is surprising because this summer my fill water was 120-140.