Increase Calcium pure product recommendations?

[tradewinds]

I've seen some products with "other ingredients" on Amazon but was looking for something pure to increase calcium. I need 18lbs per PoolMath and Cal Hypo is expensive so going with pure calcium chloride and LC combo.

PinchaPenny has this but are there other brands and products that are 100% pure also?

 

[Newdude]

I like puritech from Amazon.