| Agreed. Corals, snails, and most all other hard-shelled invertebrates build their shells by taking the free floating calcium and converting it into calcium carbonate to form their shells. In a tank deficient of calcium then they cannot build or repair their shells. Alkalinity plays a part in the buffering of calcium levels in a tank and in seawater magnesium plays a large part in the buffering process. Test for alk and if you have a SW tank then test your Calcium.
Let us know what you find and we'll take it from there.
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