2 Part Dosing; Mg not Dropping

[fort384]

I started a 2 part dosing system about 3-4 weeks ago, and over the course of the first week to 10 days, dialed in the Ca and Alk dosing to maintain 420ppm Ca and 10dKH Alk. It seems to be working well as testing for each has remained consistent over the past couple of weeks. But I have tested Mg last week and this week, and it has remained level at 1350. Shouldn't I be seeing a drop in Mg?

Should I not add the recommended Mg dose at the end of my 2 part cycle, as BRS suggests? Is there something wrong since my Mg is not dropping?

Coral are doing great - a mix of zoas, LPS, and SPS.

[ccCapt]

Mag gets used up very little compared to calcium or alk. If you had a drop of 100 ppm in calcium you would only see a drop of 5 ppm in mag. That small of a drop would be very hard to detect with a test kit.
I make my DIY alk, calcium and mag solutions and what I do is when I use up 1/2 gal of the ca and alk, I dose 1/2 cup of mag solution.

[fort384]

Thanks Larry. Yes the resolution on my kit wouldn't detect that slight of a drop. Good to know.

[danbstrong]

Originally Posted by fort384

Thanks Larry. Yes the resolution on my kit wouldn't detect that slight of a drop. Good to know.

I have a fully stocked sps 55g tank and have never added mag waterchanges with a good saltmix will keep mag up

[Phranque]

Same here.... just started 2-part about a month ago after I got my digis (alk hogs!!). I'm maintaining 11.5-12 dKH & 420-430 calc, and my mag hasn't budged from 1400-1410.
From what I understand, the mag level just prevents precipitaion & keeps it available... not really used up nearly as much.