Need help with magic Mag

Sometime back I accidentally overdosed Mg (forgot about the timer...).

The highest I've ever read it was 1800. Now I'm wondering if it just can't get higher and is now seeping back in.

Here's the numbers:

October or so it hit 1800. Oh no, I thought. I did a WC with low Mg (IO) and got it to 1770.
EDIT: SG hat hit 1.028 at this time
I figure, it'll come down eventually, right.

January 14 it had only come down to 1740. Good grief. So I change water again.

I wait a couple days to test, to let it mix in the DT and on January 18 my Mg read 1600!! Excellent I thought. That's not so high. I can wait now.
EDIT: SG by this time had been under control at 1.026

January 23 my reading was 1620. It seemed close enough ya know. An extra drop or something variation, no biggy.

Today, Febrary 10 it is 1770. No. Can't be. This Mg test was getting low so I moved to my new one. 1760. WTH.
EDIT: And my SG has gone up to 1.027, grr

Can someone please help me understand?


My jug of Mg has been with a lid now for months. I dose Ca and Alk from BRS and they've been a steady 10.5ish and 440ish.


The only thing I can think of is I must have overdosed well past 1800 but it was saturated and must have settled into the subsrate/rock whatever and after I removed it (WC) this material is now re-entering the WaterColumn... but I'm not sure if that can really happen - chemically - or not.

My head hurts.

Karma for useful help!
And even more, P's gratitude.

 

Up for you to judge how useful, but what salt mix are you using? I know reefcrystals runs higher in mg and I can not dose mg for a week or more if I do a water change.

 

I use IO, it runs low in Mg, ~1070 in my current bucket

 

Yeah, IME IO is typically around the 1100 mark.

I'm not sure what is the saturation point of Mg in sea water is. That's the real question here.

It's possible your rock absorbed the levels and is leaching it back out though.

 

Peredhil

I googled the question and cannot find any solid information relating to absorption of magnesium and later release

things I do know

reef tanks with elevated Mag levels and in 1 case I read over 2000ppm are common amongst those fighting Brypopsis - thus your 1800 should not have been the ceiling

SG - the mag level will be in proportion to the overal SG (the total number of ions dissolved in solution)

with an SG of 1.026 = 34.5ppm
the SG of 1. 027 = 35.8 ppm

thus Mag ions 1600 divide 34.5 = 46.37 ( the concentration of mag per part per million) x 35.8 ( the new SG concentration = 1660

Thus 60ppm additional, could be directly as a result of your increased SG

and if you have slightly under estimated the new SG then its possible that there is even more additional mag ions, accounted for by this simple SG equation

Steve

 

hmmm, so I'm not really sure what I should do about this.

I can ignore it and I'm thinking it'll eventually self correct. Eventually.

Seems to me like a water change doesn't really do anything... my numbers went back up to where they were to begin with.

The SG and the Mg did seem to rise hand in hand - which is what makes me think it's eeking back out of the rock/substrate... but your point on the ceiling makes me question that...

I'll keep thinking on it.

 

I would not worry about the Mg concentration just work on the salinity. People fighting Bryopsis have had their Mg up to 2200ppm. It should come down naturally from water changes and usage.

 

From what I can tell, as far as this problem is concerned, SG and Mg are the same thing...

I can lower my SG (not that I feel current reading is terrible), but it goes right back up as the Mg goes right back up. (Mg being a salt of course).

My point is, there is no fixing the SG till the Mg is fixed... at least per my current understanding...

 

I can get real technical but there's no reason to. You've pretty much figured it out on your own. For clarity for other readers, when you test salinity with a refractometer, a good portion of the "saltiness" you're testing are composed of Magnesium "salts". Magnesium alone is a metal. Magnesium Sulphate is a salt. Magnesium Chloride is a salt.

 

So I guess poor P is going to have to start doing WC again... at least till this sorts itself out.

So I've got a question - I'm predicting that what will happen is that I will lower my Mg ~100 points each time I do a WC and my SG by .01 (ish).

I feel afraid my system is in for a real treat of SG and Mg swings.

But it takes it about a month to "seep" back in so, I'm currently thinking, I should do a WC only once a month to keep these swings minimized.

Also because, if I do them too often, I won't really be removing much Mg from the system - as it's not yet back into the water column.

Does my plan of doing a WC once a month until this is resolved seem like the correct course?

Also, I should absolutely continue to auto dose my Ca and Alk right? I have been... thinking should continue... but wondering if I stopped Ca if that might not matter as the corals would transition to the Mg? I don't want to experiment with this

As a side note, I've started remixing/heating my WC water I've had in a bucket in prep for this - and my WC powerhead died. grrr.