Magnesium increasing without dosing or water change

Crashjack · Mar 13, 2018

My magnesium has been rising without dosing Mg and without a water change. This has been occurring for a while and then it either stops rising or goes down some. I have two Salifert test kits, and it doesn’t matter which one I use. Today, I measured 1620 ppm Mg. Last week was 1460 ppm and the week before, 1425 ppm. I do bi-weekly water changes and no water change between last week’s test and today’s test.

I manage Ca and alk by running all top-off water through a Kalk stirrer. I haven’t added any calcium or sodium bicarbonate in months. Salifert states that Ca levels below 500 ppm will not interfere with the test. My Ca typically runs 420-450 and today measured 440 ppm. Alk was 9.1 dkh.

I’ve been manually dosing Seachem Flourish nitrogen and phosphorus due to a dino problem. I looked back at my logs and the Mg increases seem to coincide with increases in nitrogen and phosphorus dosing. Oddly, it doesn’t seem to matter which one I dose or if I dose them both, the more Flourish I add (either or both products), the higher my Mg levels go. Is this what is causing my Mg to increase or might it be something else?

nautical_nathaniel · Mar 14, 2018

Have you changed salt brands recently?

Randy Holmes-Farley · Mar 14, 2018

Test error. There's no source for magnesium in a reef tank if you are not adding it.

Crashjack · Mar 15, 2018

nautical_nathaniel said:
Have you changed salt brands recently?

I haven’t but again, no water change.

Randy Holmes-Farley said:
Test error. There's no source for magnesium in a reef tank if you are not adding it.

I would agree if it was only one test, but Mg has progressively increased over the last month or more, and I’ve used two different Salifert test kits. Is it possible that theFlourish contains a significant amount of Mg or maybe something that might interfere with the test results?

Randy Holmes-Farley · Mar 15, 2018

Crashjack said:
I haven’t but again, no water change.

I would agree if it was only one test, but Mg has progressively increased over the last month or more, and I’ve used two different Salifert test kits. Is it possible that theFlourish contains a significant amount of Mg or maybe something that might interfere with the test results?

Which Flourish?

Crashjack · Mar 15, 2018

Randy Holmes-Farley said:
Which Flourish?

Seachem Nitrogen and Phosphorus.

Randy Holmes-Farley · Mar 15, 2018

Crashjack said:
Seachem Nitrogen and Phosphorus.

Neither of those are supposed to contain magnesium, so I expect they are not a source.

Aside from test error (which i still think is the logical explanation), the other thing that raises magnesium to rise is a salinity rise.

A sg rise from 1.024 to 1.026 will boost magnesium from, say, 1200 to 1300 ppm.

Topping off with water that contains a lot of magnesium is also a possibility, although a bit far fetched.

Crashjack · Mar 15, 2018

Randy Holmes-Farley said:
Neither of those are supposed to contain magnesium, so I expect they are not a source.

Aside from test error (which i still think is the logical explanation), the other thing that raises magnesium to rise is a salinity rise.

A sg rise from 1.024 to 1.026 will boost magnesium from, say, 1200 to 1300 ppm.

Topping off with water that contains a lot of magnesium is also a possibility, although a bit far fetched.

Every time I make a batch of saltwater (every two weeks), I recalibrate my refractometer and test my display water as well as the new water. My sg hasn’t changed. Also, my top-off is RO/DI. Is it possible my BRS kalk might have Mg accidentally mixed in? What is also weird is that i used to get normal, slowly falling Mg readings. I would add Mg when needed, levels would rise and then slowly fall again. Now, levels stay about the same or increase from week to week even though I haven’t added any Mg in a while. I also haven’t changed brands of test kits, and the older Salifert kit is the same one that used to get the normal readings.

chipmunkofdoom2 · Mar 15, 2018

How are you calibrating your refractometer? Are you using a salinity standard specifically designed for use with refractometers?

Crashjack · Mar 15, 2018

Yes. I’m using the 35ppt solution BRS sells. I also purchase a new bottle every several months and verify the sg matches the old bottle.

Randy Holmes-Farley · Mar 16, 2018

Crashjack said:
Every time I make a batch of saltwater (every two weeks), I recalibrate my refractometer and test my display water as well as the new water. My sg hasn’t changed. Also, my top-off is RO/DI. Is it possible my BRS kalk might have Mg accidentally mixed in? .

No, unless it is completely a magnesium product by mistake. Magnesium doesn't dissolve into limewater.

Crashjack · Mar 16, 2018

Randy Holmes-Farley said:
No, unless it is completely a magnesium product by mistake. Magnesium doesn't dissolve into limewater.

I thought I remembered reading something like that in one of your articles but couldn’t remember exactly how Mg was affected. I guess I will continue to test weekly and see what happens.

Randy Holmes-Farley · Mar 17, 2018

Crashjack said:
I thought I remembered reading something like that in one of your articles but couldn’t remember exactly how Mg was affected. I guess I will continue to test weekly and see what happens.

That sounds good.

JDJP · Apr 11, 2018

I have the same issue, i use kalk in my ato with 0tds rodi water from my well. No way it could read 0tds and still contain mag correct?

Ive run a coupke triton tests and havent been doing water changes for several months.

A couple similarities i see, i use brs kalk, brs calcium chloride.

Was using baking soda for alk bumbs every day now that my kalk isnt keeping up.

Randy Holmes-Farley · Apr 11, 2018

JDJP said:
I have the same issue, i use kalk in my ato with 0tds rodi water from my well. No way it could read 0tds and still contain mag correct?

Ive run a coupke triton tests and havent been doing water changes for several months.

A couple similarities i see, i use brs kalk, brs calcium chloride.

Was using baking soda for alk bumbs every day now that my kalk isnt keeping up.

How much did magnesium rise in the Triton tests?

JDJP · Apr 12, 2018

I was trying to keeo it around 1300 and its gone up to around 1500 and stayed without dosing

Randy Holmes-Farley · Apr 12, 2018

JDJP said:
I was trying to keeo it around 1300 and its gone up to around 1500 and stayed without dosing

If real, rather than testing error, that can only be from dosing or water changes. Magnesium does not rise like that on its own.

Magnesium testing error is also very common.

TexasTodd · Nov 7, 2018

Hey Randy, do you have a favorite hobby magnesium test kit to recommend? PM if you want.
I picked up a Salifert and am not confident it's reading correctly.
Thanks,
Todd

MnFish1 · Nov 7, 2018

There is a Margin of error in each test kit. If your tank looks ok - maybe 'not worry about it'. I have gone to much less testing - with no dire results - except its a lot cheaper....

Drewbacca · Apr 4, 2019

Came across this because im having the exact same issue. I only dose kalk, And use salifert mg kit (3 test in a row yesterday), my salinity is always good and check daily with properly calibrated refractometer. I AM however doing weekly 15% water changes With red sea coral pro, but that would make it stay more regulated I wld think. My mg is at 1560-1600. Calc 445 449 alk 8.5 ph 7.9 8.0 nitrate 0 phos 0.0. I wouldnt care too much if everything was growing fine but My corals arent growing and even took a downhill turn past few days. Esp, torch frag keeps receeding and cant figure out why. I feed alot & even target feed. So checked mg, which I hadnt tested often.