I've been fighting a red algae cyano looking bugger that nothing I do can stop. Chemiclean does absolutely nothing to it. If i remove it or disturb in any way, it reforms within a day. It mostly sticks to just the sand and spreads onto any other type of algae, of which there is extremely little, in the tank. Ive noticed dark spots under the sand through the glass and am wondering if these could be related or are something to worry about in general. Nitrates and phosphates are always near 0 even on very accurate tests. Its a coral tank, all corals are happy and fish are too. Running activated carbon and a protein skimmer.