I have used them in the past. It is a Hiatt product. That description is incorrect though, well bs really. The blocks just slowly dissolve releasing calcium plus the trace elements. They will dissolve too quickly if placed in any current and Hiatt recommends you bury them in the sand.

It is calcium chloride which can give you problems if you use it alot in an unbalanced fashion therefore I don't use them. Decent product for small tanks or to use to raise calcium up to 400-450 and then start using a balnced additive.