Why does reef crystals only have 320 Ca?

[StrategicReef]

I have come to acknowledge the fact that reef crystals only mix up to have around 300-320 Ca at my household. I bought 2 buckets 1 year a part and same thing happens, maybe some Ca precipatated but I am not the only one finding Ca levels low this with this salt when I do a search.

It's a good salt for me from a price stand point and I have good luck raising the calcium to 375-400 with reef complete. I need a cheaper way to supplement the calcium in the freshly mixed water so should I use turbo calcium?