what would prevent MG from dropping - Ive done BIG h20 changes


bona-fide REEF NUT
Manhattan Reefs
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So I had an accidental MG overdose - it happened with a dosing pump that apparently wasnt working, (although I didn't know that at the time), and I increased the MG dose gradually- when all of a sudden....my corals started throwing SNOT and my MG went from 1100-ish to I lost count of the drops.

I am running a 180g display, 40 gallon sump. I stopped all dosing, did a 50 gallon water change, then did (a week later) another 40, and two days later another 40gallons. my MG is still testing off the test-kit chart, although after the first water change the corals all stopped snotting and mostly are recovering. (A favia, a few acans, still seem to be suffering)

Any idea of what could keep my MG high? Is it possible that there is MG in my RODI water? How about can a Mag Pump - can it throw off or leach MG? I am at a loss.

Also, I changed from ESV salt to Tropic Marin for the last water change, just in case.


thank u



Bomb Technician (EOD)
Manhattan Reefs
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First and foremost, test your new seawater mix before you add it to see what it says. Maybe it is your kit or you are not using it correctly. What was the doser adding exactly, how much was added from the doser. If your Mg ++ over dose gave ~4000 ppm your water changes would still leave it at ~2300 ppm , almost 2x natural seawater.

Alfredo De La Fe

Senior Member
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Upper West Side
Corals can tolerate Mg over 1500ppm. I would just keep doing water changes as normal. Chances are that you dosed a lot more Mg than you realized.

Where in NYC are you? I have been slowly raising my Mg and just got used to using the stupid Mg test kit.