Mag increasing but I'm not adding any, confused on the chemistry

[slojmn]

I have slowly been bringing my alk and calcium up a bit, alk from 8.4-8.7 dKH and calcium from 380 ish to 400 ppm over the past few weeks. I notice my mag has increased as well 1370 up to1430, but I'm not dosing for that. No water change either, how does that happen? Just curious about the chemistry behind the mag rising without any additions. I'd like to keep all where it is and get calcium up a bit more at this point, but I was feeling mag was fine where it was. I am just surprised the mag has risen.

 

[Brew12]

I have slowly been bringing my alk and calcium up a bit, alk from 8.4-8.7 dKH and calcium from 380 ish to 400 ppm over the past few weeks. I notice my mag has increased as well 1370 up to1430, but I'm not dosing for that. No water change either, how does that happen? Just curious about the chemistry behind the mag rising without any additions. I'd like to keep all where it is and get calcium up a bit more at this point, but I was feeling mag was fine where it was. I am just surprised the mag has risen.

What are you using to raise alk and calc?

 

[slojmn]

What are you using to raise alk and calc?

2-part dosing

 

[madweazl]

Check your salinity.

 

[slojmn]

Salinity is stable and in line, 1.026.

 

[taricha]

I notice my mag has increased as well 1370 up to1430, but I'm not dosing for that.

I'll just point out that's less than a 5% discrepancy. Which is pretty dang low for any hobby test kit.
(I don't think you Mg actually went up)

 

[Randy Holmes-Farley]

If it is not a salinity change that is raising the magnesium, it it likely testing error. It doesn’t just rise on it’s own.

 

[Stigigemla]

Sometimes It can be a magnesium import/export from live rock.
I often see that new live rock consumes some magnesium. I have seen tanks where the magnesium level has decreased around 100 mg/l the first month without corals consuming it. After a Year or so that has balanced.
And lately I have had 2 customers changing salt brand to get lower magnesium just to find that a week after the water change the value is back or almost back again.

 

[slojmn]

If it is not a salinity change that is raising the magnesium, it it likely testing error. It doesn’t just rise on it’s own.

Kind of what I thought as well. Since it is a small amount it could be related to a change in salinity from 1.0224 to 1.026...this is the range I see when I use my hydrometer to check salinity once every few weeks on the tank. I don't really trust my salinity probe as it bounces all over, lol.

 

[Stigigemla]

Try putting some water in a glass and test it with the probe away from tank water.
Many times the probe interferes with other electrical things close to it.