Troy, the corals don't feed on phyto, but the anemone crab may, depending on species. The feathers may also eat it. The corals may eat bits of fish food or plankton generated from pods and such, and the anemones should be fed directly with meaty foods every now and then.
None of those things uses calcium in appreciable amounts, and regular water changes should keep your levels right on target.
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Brad
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