I noticed when I ran co2 24/7 my sand bed would solidify. Read somewere that mg has to be a minimum of 1300 or the corals can't use up the calcium as the proper chemical ratio is required for this to take place.With your calcium on the high side maybe try bumping up your mg a bit. I've run mg as high as 1500 and alk at 11 and had the best growth. Your alk is way to low.
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Sebae
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