Mg shot up 100 ppm in a week?

[Kris 2020]

I do currently dose magnesium. I started again in late august when my levels dropped to 1215-1220 ppm. I dosed manually over a couple weeks to get it up around 1300. Then I set up my dosing pump for 3 times daily, 7 days a week. Testing (salifert) showed:
9/5 1260
9/12 1300
9/19 1275
9/26 1290
10/3, 10/10, 10/17, 10/25 all 1275
icp test from water collected 10/25 showed 1340
11/2 1282
11/9 1395!!! BAM

any thoughts? Other results from today:
salinity 1.022 (Working to bring this up slowly, had poorly calibrated refractometer)
temp 78.4
ph 8.29
nitrate 4.3
phosphate .04
alk 8.9
calcium 446

i haven’t made changes to my alk or cal dosing. I did remove 7 bta’s. And I halved my cheato about 2 weeks ago. But I still have a crap ton.

 

[DC Reefer]

1395 shouldn’t hurt anything. I run mine at 1400-1500. I would test again and make sure it wasnt an error and then test again tomorrow to see if it is still increasing. If it is going up decrease the dose or stop dosing until it gets back where you want it.

 

[Kris 2020]

1395 shouldn’t hurt anything. I run mine at 1400-1500. I would test again and make sure it wasnt an error and then test again tomorrow to see if it is still increasing. If it is going up decrease the dose or stop dosing until it gets back where you want it.

Thanks! I cut back the dose a bit, and I did test twice since it was an unusual result, they both showed the same. I’ll just keep an eye on it and adjust as needed I guess, I get so used to my same-ish results when testing that changes startle me. I’ll be testing lots as I bring my salinity up to where it belongs, as I’m sure I will need to adjust alk and cal doses in response to that.

 

[DC Reefer]

If you are increasing salinity it will bring all your elements up also. My LFS will do free water tests of the basics. if yours will you can have them test which will give you another datapoint.

 

[MnFish1]

I do currently dose magnesium. I started again in late august when my levels dropped to 1215-1220 ppm. I dosed manually over a couple weeks to get it up around 1300. Then I set up my dosing pump for 3 times daily, 7 days a week. Testing (salifert) showed:
9/5 1260
9/12 1300
9/19 1275
9/26 1290
10/3, 10/10, 10/17, 10/25 all 1275
icp test from water collected 10/25 showed 1340
11/2 1282
11/9 1395!!! BAM

any thoughts? Other results from today:
salinity 1.022 (Working to bring this up slowly, had poorly calibrated refractometer)
temp 78.4
ph 8.29
nitrate 4.3
phosphate .04
alk 8.9
calcium 446

i haven’t made changes to my alk or cal dosing. I did remove 7 bta’s. And I halved my cheato about 2 weeks ago. But I still have a crap ton.

1. Recheck your test.
2. Turn off the Mg dosing.
3. IMHO - you're over thinking it. A Mg of 1395 is not critical - if you stop dosing it will fall slowly on its own (i.e. no need to worry or 'BAM'.. I haven't checked my Mg for at least 3 months. But - I also do periodic water changes - that keep it in line.

PS. how are you bringing up your SG? If you're adding a salt mix - you're also adding Mg.

 

[Kris 2020]

If you are increasing salinity it will bring all your elements up also. My LFS will do free water tests of the basics. if yours will you can have them test which will give you another datapoint.

Nearest saltwater lfs is over an hour away, unfortunately.

 

[Kris 2020]

1. Recheck your test.
2. Turn off the Mg dosing.
3. IMHO - you're over thinking it. A Mg of 1395 is not critical - if you stop dosing it will fall slowly on its own (i.e. no need to worry or 'BAM'.. I haven't checked my Mg for at least 3 months. But - I also do periodic water changes - that keep it in line.

PS. how are you bringing up your SG? If you're adding a salt mix - you're also adding Mg.

Topping off with saltwater instead of rodi. I just started that this past Saturday tho.
I’m sure I am overthinking it, you are right, I just like to know WHY...and this hobby doesn’t always supply the why lol. TALK TO ME TANK, I MUST KNOW THE REASONS FOR YOUR SUBTLE CHANGES. I need a tank whisperer.

 

[Cabinetman]

It’s like what was mentioned. You raised your salinity. Likeky the salt mix has a good concentration. I’ve seen it happen in my system on my trident after adding some salt.

 

[Randy Holmes-Farley Verified Community Expert]

I don't know what happened as I'm not sure that any specific measurement is accurate.

The magnesium bump is test error, which is very common, unless the salinity rose substantially that day.

Here's the extent of salinity effect on magnesium:

Suppose you are at 1280 ppm magnesium and the specific gravity is 1.020 (that is actually very high in magnesium for that salinity, but that's a different issue).

Then you top off with seawater to raise the specific gravity to 1.022. How much did magnesium rise?

It rose from 1280 ppm to about 1280 * 22/20 = 1408 ppm.

So salinity can have a huge impact on magnesium.

 

[MnFish1]

Topping off with saltwater instead of rodi. I just started that this past Saturday tho.
I’m sure I am overthinking it, you are right, I just like to know WHY...and this hobby doesn’t always supply the why lol. TALK TO ME TANK, I MUST KNOW THE REASONS FOR YOUR SUBTLE CHANGES. I need a tank whisperer.

Ok ok - thats probably why its going up - as will all of the other elements. Of course thats what you 'want' - right? You want all of the element levels at teh correct levels as they are when yoru SG eventually gets to 1.025. This means that - by doing the changes (or using the ATO) - to get the S.G. up - you will also raise all of your parameters (alkalinity, Ca, Mg, etc etc) - so - I would consider stopping your dosing (of Mg) completely and watching Ca and Alkalinity carefully as you are are doing it. Just my opinion. When I had this issue - I mixed up some water at 1.028 or so - and then daily removed a 5 gallons of tank water - and added 5 gallons of the 'new' water. with a 100 gallon tank - everything was 'fine' after a week. Then I resumed the dosing, etc that I usually was doing. note - I do not ever dose Mg - except as per the BRS system - which is - 'each time you use a gallon of Ca/Alk solution add xxxx Mg so4/Cl mixture.

 

[MnFish1]

Topping off with saltwater instead of rodi. I just started that this past Saturday tho.
I’m sure I am overthinking it, you are right, I just like to know WHY...and this hobby doesn’t always supply the why lol. TALK TO ME TANK, I MUST KNOW THE REASONS FOR YOUR SUBTLE CHANGES. I need a tank whisperer.

I don't know what happened as I'm not sure that any specific measurement is accurate.

The magnesium bump is test error, which is very common, unless the salinity rose substantially that day.

Here's the extent of salinity effect on magnesium:

Suppose you are at 1280 ppm magnesium and the specific gravity is 1.020 (that is actually very high in magnesium for that salinity, but that's a different issue).

Then you top off with seawater to raise the specific gravity to 1.022. How much did magnesium rise?

It rose from 1280 ppm to about 1280 * 22/20 = 1408 ppm.

So salinity can have a huge impact on magnesium.

I don't understand - he was dosing Mg - and using ASW in the top off - why according to your reasoning above - would that not have raised the Mg? Or were you saying what he has done so far cant explain that much of a rise? Just curious

 

[Randy Holmes-Farley Verified Community Expert]

I don't understand - he was dosing Mg - and using ASW in the top off - why according to your reasoning above - would that not have raised the Mg? Or were you saying what he has done so far cant explain that much of a rise? Just curious

I'm saying that lots of people see rises and falls to magnesium that are test error, and that cannot be ruled out here.