Does Salinity Fluctuations Impact Magnesium Levels

[Duncan Tse]

Last week I tested my parameters as follows

Salinity = 1.026
Mg = 1410

Fast forward to a week and I tested my parameters

Salinity = 1.025
Mg = 1215

I know there is no way that my magnesium consumption is that high as my tank only takes up 0.3 dkh alk and 2 ppm cal a day

What should I do at this point?

 

[X-37B]

Retest the mag. Testing error.

 

[Duncan Tse]

Retested again and I got 1170

I don't understand what's going on with my system it seems to be depleting Mg so fast

April 12 = 1170
April 19 = 1470 - Dosed Mg and bumped it to this level in a week
Arpil 26 = 1500 - Changed carbon
May 2 = 1380
May 10 = 1410 - Changed carbon
May 17 = 1170

Seems to me Mg holds steady for 2 weeks and then it drops

Holds steady for another week and then it drops again

Using soda ash for alk and calcium chloride for ca
Dosing at 7mL each daily

Weekly water changes at 10% using regular IO salt

Change 1/2 cup carbon in a reactor every 2 weeks

Another observation is could it be that the changing of carbon will reduce Mg? Seems to me like when I change my carbon during a water change the next week Mg drops

 

[Duncan Tse]

May have figured out the problem

I premix 20 gallons of saltwater for my water change and just found out the batch of IO salt was mixing at 1050ppm magnesium

Would you say this was the cause as to why my Mag levels kept decreasing over time?

 

[Randy Holmes-Farley Verified Community Expert]

I think the cause is test error, which is very common. Even in the new salt water.

 

[Duncan Tse]

I think the cause is test error, which is very common. Even in the new salt water.

May be bad test kit? I just ordered another salifert Mg test kit so I'll see what numbers I get

 

[Duncan Tse]

Just a quick update I bought a new salifert magnesium test kit and I got 1140 ppm Mg in my waterchange barrel. I mix up 20 gallon at a time and maybe I did not shake the bag well enough as I just scoop it out. This likely caused my Mg levels in my tank to decrease

 

[reefluvrr]

I too have problems getting consistent Magnesium test results.
Right now I use both Salifert and Red Sea Pro.

Honestly, I ended up going to my local fish store to ask them to test my mag to compare to my result.

Maybe you can have your significant other do the test and see if they get the same/different result?

 

[Duncan Tse]

I too have problems getting consistent Magnesium test results.
Right now I use both Salifert and Red Sea Pro.

Honestly, I ended up going to my local fish store to ask them to test my mag to compare to my result.

Maybe you can have your significant other do the test and see if they get the same/different result?

The bad batch was from a 200 gallon IO salt box that I ordered. The box came with 5 bags of IO salt.

I opened up a new bag in the same box and mixed it in 5 gallons of water. Tested the parameters and I got alk 10.2, cal 400, mg 1320. Used 2 different Salifert Magnesium test kits and still get very similar Mg levles. This was more in line of what IO salt mixes at so I feel pretty confident it was a bad batch.

Lesson learned as to always test your waterchange water as some of my corals are not looking their best probably because of me bumping Mg to 1400+ and then having it swing down with every water change.