Randy Holmes-Farley
Reef Chemist
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My Tank Thread
Ah gotcha. I hear the same thing about reef crystals (brown residue) but I have always cleaned my brute can after every water change so haven't noticed any.
FWIW, I'm not sure that brown residue is calcium carbonate, that is present in normal IO and Red Sea Coral Pro. It may be related to the organic materials they add, but I'm not sure.