A few months ago I completely stopped dosing magnesium in my 90G mixed reef, since I have consistently tested levels over 1600 ppm (I'd like to keep it between 1250-1350). Since cutting off dosing a couple of months ago, I still see levels in the 1600's, and I'm wondering what on earth keeps that level so high. With auto-dosing, calcium stays around 420 ppm, and Alk is a little low at about 7.4 dkh (slowing trying to raise it to between 8-9, as well as get pH up to about 8.2).
My corals are healthy and growing so I assume they're uptaking magnesium, though I don't recall if they typically uptake Mg at the same rate as Ca and Alk. I'm beginning to wonder if there is some other source of Mg in my system. I only do water changes every couple of months so I don't know if it's my salt mix. My RO/DI top off water reads 0 TDS. Is it possible my rocks or sand are leaching Mg into the system? I've hard that oolitic sand and some Lake Bonneville tufa rock can do this, and I do have several inches of the sand in my sump, and a few rocks in the system. But I'm not sure how reliable these theories are, since it seems they have been somewhat convincingly debunked recently (though I can't site any sources - it's just my recollection). Any insight would be most appreciated!
Here's an annotated recent FTS. I've added a few new frags, and haven't labeled all the zoanthids or mushrooms. (Not sure how to get it to display any larger)
Edited by Deluxe247 - December 06 2020 at 3:09pm
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