What is happening to my magnesium?

[Vinstr]

Hello all,

I have a 120 gallon mixed reef tank. Salinity is 1.026. Calcium is 420 alkalinity is 8.9. Magnesium is 1170. I dose 35 mg of All for Reef which keeps my calcium and alkalinity stable. my magnesium however drops to under 1100 if I don’t dose extra magnesium. Problem is I am dosing 50 ml. milliliters of Brightwell magnesium P and it only gets my magnesium up to 1170. From everything I’m reading here, that’s a lot of magnesium and with the levels of calcium and alkalinity my tank is consuming, there’s no way it could be consuming that much magnesium. Everything looks fine in the tank. I use Salifert test kits and thought it might be the test kit so I bought a brand new test kit and got the same results. Everyone seems to respect the salifert test kit so I don’t think it could be off that much. I don’t see any precipitation in the tank. My questions are: is it possible my tank is really consuming that much magnesium? If not, where is it going because my magnesium levels are not rising? I use instant ocean reef crystal salt and it has extra magnesium too. I do a 15% water change every week. I am so dumbfounded about where all this magnesium is going and worried that it might be too much and be dangerous. Any help would be greatly appreciated!

 

[KrisReef]

If you were not doing a water change every week I would worry.

How much Mg is in reef crystals? I don't know where your Mg is going, or if the Salifert isn't correct?

Whatever, here is an old article on Mg that might help:

https://reefkeeping.com/issues/2006-07/rhf/index.php

 

[BryanM]

reef crystals appears to be in teh 1450 range.

From what I've read testing mag is hard. If you're worried I'd do an ICP test and let them do that for you.

if things are looking good, then I'd do the ICP for peace of mind, and I suspect the number comes back higher than you're testing at.

 

[Vinstr]

Thanks for your help. What is an ICP test? But that still wouldn’t explain what is happening to all the magnesium I have been putting in because the test is the same every time after 50ml. a day for months. Even if the test was off 200 off how is 50ml. A day not increasing it? Can my tank be consuming that much? I have a refugium with chaeto and a lot of corals I should let you know too. I heard chaeto consumes magnesium I think?

 

[UMALUM]

No the tank is not consuming that much. Make sure your mixing to 35 and test a fresh batch. I had a couple bad buckets of rc mixing in the 9s so it's possible. There have been reports of bad kits as well. Also you can try rolling the bucket or mixing the whole bag at once to see if that helps.

For the record rc does not mix at 1450 no matter what anyone claims. Personally I think the company is slipping/cutting corners. I have 2 buckets currently mixing in the 12s at the moment. It's a shame but after 25 years I'm giving up on them.

 

[gbroadbridge]

Thanks for your help. What is an ICP test? But that still wouldn’t explain what is happening to all the magnesium I have been putting in because the test is the same every time after 50ml. a day for months. Even if the test was off 200 off how is 50ml. A day not increasing it? Can my tank be consuming that much? I have a refugium with chaeto and a lot of corals I should let you know too. I heard chaeto consumes magnesium I think?

Your test kit is faulty or your salinity is very low.

How are you checking salinity? Have you calibrated your salinity instrument?

 

[Vinstr]

Yes I just bought a new refractometer and hydrometer thinking it must the salinity but both now show 1.026

 

[BryanM]

Icp tests.

Icp Test - Bulk Reef Supply

Shop Icp Test at Bulk Reef Supply and get rewarded on every purchase with our Preferred Reefer program.

www.bulkreefsupply.com

 

[Randy Holmes-Farley]

Have you ever used that kit on your new salt water?

Testing may not be worth the bother:

Just say NO to magnesium testing: RMM is born

OK, this thread has been many years in the making, and I'm posting it here since folks in the chem forum are probably already tired of all the threads relating to problematic magnesium testing. I'm going to propose a method, let's call it the Randy Magnesium Method, or RMM for short. All good...

www.reef2reef.com

 

[Vinstr]

I will make some water this weekend and test the new water. Good idea and thank you.

 

[twentyleagues]

Do you have a lot of new coralline growth? My understanding is coralline takes up a lot of mag and alk but not much calc. What is a lot of mag?? I dont know maybe a good portion of what you are dosing, seems like a lot though.

 

[Randy Holmes-Farley]

Do you have a lot of new coralline growth? My understanding is coralline takes up a lot of mag and alk but not much calc. What is a lot of mag?? I dont know maybe a good portion of what you are dosing, seems like a lot though.

That’s not true. Coralline still takes up 10x as much calcium as magnesium. Most hard corals take up much less.

 

[twentyleagues]

That’s not true. Coralline still takes up 10x as much calcium as magnesium. Most hard corals take up much less.

Huh I must have been drinking when I read that . Ill have to go see if I can find where I read that and got that idea stuck in my head. It was very recently too.

Is the mag part correct? Maybe I adlibbed the calc part on my own.....?

 

[get-salty]

Highly recommend buying the ATI ICP test kit and send it in for a water analysis, its is $45 bucks on BRS. It is a prepaid package that you send back to their lab along with 3 samples of your tank water and 1 sample of your RO water. You will get a result within 7-10 days. Good luck and happy reefing !

ATI ICP-OES Water Analysis

Scientific testing for a complete picture of aquarium health Knowing what’s going on inside your tank’s water shouldn’t be a complicated process. Get a comprehensive look at your tank’s water chemistry using ATI ICP testing. ICP-OES testing has become a mainstay tool of modern reefing. With it...

www.bulkreefsupply.com

 

[Randy Holmes-Farley]

Huh I must have been drinking when I read that . Ill have to go see if I can find where I read that and got that idea stuck in my head. It was very recently too.

Is the mag part correct? Maybe I adlibbed the calc part on my own.....?

Coralline uses more mag than most anything else in reef tanks, and is the reason for the high end of my RMM method, with mag added at 10% of the calcium rate. Most corals uses proportionally less and some use far less. Hence the range for RMM being lower when coralline is not the4 main driver of alk and calcium demand.

The reason coralline uses more is that it is not depositing aragonite, as corals do, but a different form of calcium carbonate called high magnesian calcite.

I show a bunch of organisms magnesium contents here:

Aquarium Chemistry: Magnesium In Reef Aquaria

This article details the nature of magnesium in seawater, how it is added, measured, and removed from marine aquaria, and how it impacts the maintenance of calcium and alkalinity.

reefs.com

 

[Hallowhead]

I'd also buy a second mg tester - salifert is a good one

 

[twentyleagues]

Coralline uses more mag than most anything else in reef tanks, and is the reason for the high end of my RMM method, with mag added at 10% of the rate. Most corals uses proportionally less and some use far less. Hence the range for RMM being lower when coralline is not the4 main driver of alk and calcium demand.

The reason coralline uses more is that it is not depositing aragonite, as corals do, but a different form of calcium carbonate called high magnesian calcite.

I show a bunch of organisms magnesium contents here:

Aquarium Chemistry: Magnesium In Reef Aquaria

This article details the nature of magnesium in seawater, how it is added, measured, and removed from marine aquaria, and how it impacts the maintenance of calcium and alkalinity.

reefs.com

Ok so I just confused the calcium part a bit.

 

[Randy Holmes-Farley]

I'd also buy a second mg tester - salifert is a good one

I personally would not recommend that, but it's an OK kit to try. I do not intend to measure magnesium at all in my tank, except if it gets done incidentally when getting an ICP.

That said, if one has a tank and is not doing any significant water changes, then it may be needed once in a while.

 

[Hallowhead]

I personally would not recommend that, but it's an OK kit to try. I do not intend to measure magnesium at all in my tank, except if it gets done incidentally when getting an ICP.

That said, if one has a tank and is not doing any significant water changes, then it may be needed once in a while.

I was doing water changes once a month using instant ocean (1,350) for salt, my mag was testing at 1,150 and despite the water changes it was not increasing. Which is not within range so I started dosing Mg in addition to my Cal and kH. Are you implying that 1,150 is acceptable and I shouldn't have and or still be chasing range ?

 

[Randy Holmes-Farley]

I was doing water changes once a month using instant ocean (1,350) for salt, my mag was testing at 1,150 and despite the water changes it was not increasing. Which is not within range so I started dosing Mg in addition to my Cal and kH. Are you implying that 1,150 is acceptable and I shouldn't have and or still be chasing range ?

I think it likely that the difference is test error or a salinity difference. Getting such a large difference between the new salt water and the tank would require a lot of alk and calcium demand for an extended period with no magnesium additions.

It is not too hard to put a conservative estimate on that effect, so lets do it, then you can assess whether your scenario might be real or not.

Suppose you are dosing a fairly high alk rate of 2 dKH per day. That means calcium is being consumed at about 14 ppm per day, and magnesium at no more than 1.4 ppm per day.

Assuming that you add no magnesium at all, this is what would happen at fixed salinity over time when doing a 30% water change each month. Thus, I do not see it getting to the value you quote.

Month Magnesium
0 1350
1 1320
2 1298
3 1283
4 1273
5 1266
6 1261
7 1257
8 1255
9 1253
10 1252
11 1251
12 1250