[Reefiez]

I got my hands on some pharm grade calcium chloride 2 hydrate (99%-103% assay).

I am not a chemistry person, so I am looking for some input on whether my calculation or assumptions are correct.

Randy's recipe uses dowflake, which is 77-80% calcium chloride (by weight).

My first instinct is that mine is ~100%, which is ~20% purer than Randy's. So I just decrease the amount of powder to dissolve accordingly. Instead of 2.5 cups per gallon, just 2 cups.

But then I thought, I think I'm missing something, where did the 2 water molecues go?

So I googled a periodic table and searched the atomic weight of the elements, and calculate the calcium chloride portion (assuming 100% purity for simplicity).

CaCl (H2O)2 will have an atomic weight of 111.56
CaCl has an atomic weight of 75.53

Assuming 100% purity, CaCl by weight is 0.677, or 67.7%.

67.7% is about 10% LESS than Randy's Dowflake of 77-80%.

Does this mean I should add the ~10% MORE, so 2.75 cups?

I haven't touched chemistry for over a decade, am I over-thinking this? Could someone point me in the right direction?

Thanks a lot!