Just say NO to magnesium testing: RMM is born

[BeanAnimal]

Reef Advantage Calcium also has 17mg of magnesium. If you have a coralline algae and lots of it boosting maybe needed if you have LPS dominant tank

You don’t have to test magnesium as frequently as you would test calcium/alk
Dosing by hand could be more of problem but if you have dosing pumps it’s less of a bother as you know magnesium is in its range without needing to test

I think you may have missed the point.

Magnesium depletes pretty much in balance with calcium, so as you maintain calcium you maintain magnesium at the about ~7% of that calcium rate. If you do that, then it will pretty much stay in balance and you don't need to test it.


That means that if you use a balanced additive solution (ATI, Triton, DIY 3 part, etc.) it will stay balanced and you don't need to test. Some of us use dosing pumps, manual dosing, etc.

It also means that if you are dosing magnesium at some other percentage of calcium and doing so based on "testing" then you re likely and iteratively creating more imbalance than you are correcting for.

Randy's point (he can correct me if I am wrong) was that the depletion ratio based on calcium consumption is likely more reliable than any manual test you are conducting.

 

[GARRIGA]

Keep it simple works for me.

 

[marcus aurelius]

 

[Snoopy 67]

Bean, Thanks for that. It's the best explanation of the relationship between the two I've heard and can completely understand.

 

[Spare time]

What about for tanks with refugiums that may take up magnesium independent of calcium?

 

[Randy Holmes-Farley]

What about for tanks with refugiums that may take up magnesium independent of calcium?

Normal refugia do not do that.

There's some discussion of mangroves and magnesium, but I'm not convinced that's a substantial issue in most reef tanks that have mangroves.

 

[taricha]

Makes a lot of sense. We don't test sulfate either.
The uptake is small, the amount in the water is huge.

@rtparty what was the range of Mg in your big salt mix tests?

So @Randy Holmes-Farley , do you think that the importance of Mg in stabilizing supersaturated Ca in saltwater is overstated and risks of precipitation from Mg too low are actually not worth thinking about too much?

 

[rtparty]

Makes a lot of sense. We don't test sulfate either.
The uptake is small, the amount in the water is huge.

@rtparty what was the range of Mg in your big salt mix tests?

So @Randy Holmes-Farley , do you think that the importance of Mg in stabilizing supersaturated Ca in saltwater is overstated and risks of precipitation from Mg too low are actually not worth thinking about too much?

ATI ICP had them range from 1221 to 1562mg/l. My own testing ranged from 1260 to 1650ish.

Couple caveats, the 1650ish was my best guess as I assumed I messed up the test on that one. The 1562 from ICP was the one I got 1650ish. So at least I got that it was high LOL. The 1221 from ICP was 1275 on my own test. My lowest test of 1260 came back at 1283 on ICP.

How does ppm translate to mg/l or are they identical?

 

[Randy Holmes-Farley]

ATI ICP had them range from 1221 to 1562mg/l. My own testing ranged from 1260 to 1650ish.

Couple caveats, the 1650ish was my best guess as I assumed I messed up the test on that one. The 1562 from ICP was the one I got 1650ish. So at least I got that it was high LOL. The 1221 from ICP was 1275 on my own test. My lowest test of 1260 came back at 1283 on ICP.

How does ppm translate to mg/l or are they identical?

1 ppm = 1 mg/kg

Since 1 L of seawater weighs about 1.024 kg, they are close, but not identical.

 

[Fish Styx]

Normal refugia do not do that.

There's some discussion of mangroves and magnesium, but I'm not convinced that's a substantial issue in most reef tanks that have mangroves.

I have a satellite mangrove tank / refugium with a DSB and haven't noticed any deleterious effect on magnesium levels.

 

[t5Nitro]

I like this method. I hate testing magnesium.

Oh man. All testing sucks.

 

[BeanAnimal]

I have a satellite mangrove tank / refugium with a DSB and haven't noticed any deleterious effect on magnesium levels.

Photos? I have contemplated doing this for 20 years

 

[gbroadbridge]

I test Mg every month or two, but only because I don't really do water changes and it gives a couple of data points between 6 monthly ICP-OES tests.

 

[Fish Styx]

Photos? I have contemplated doing this for 20 years

 

[brclark82]

Is testing your salt mix once per batch of slat allowed under RMM or are the test so inaccurate it doesn’t matter anyway. I am convinced I got a low batch of mag IO salt but who knows

 

[dwest]

This makes sense. I’ve used kalk and 2 part (plus water changes) for 30 years. I’ve added magnesium (based on monthly testing) a grand total of once! Why am I testing???

 

[Barncat]

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 methods need a catchy name.

Here it is.

1. NEVER measure magnesium. If it comes free from an ICP, sure, take a look. It's probably fine anyway. Don't buy or use a kit. Chances are the results are not very reliable, and most of the time, if there is a value out of the range of acceptable, it is more likely an error of some sort than a real result.

2. Use a decent salt mix at a decent salinity that has a starting level of magnesium and calcium that you like. If you cannot find one, it is easy to add a fixed amount of magnesium to a salt mix. I did that for many years, and rarely measured the tank itself.

3. ANY time that you add calcium, add 5-10% as much magnesium (so for 10 ppm calcium, add 0.5 - 1 ppm magnesium). If coralline is the main user of alk in your tank, use the 10%, if corals are, use 5%. A lot of products, like commercial two parts, AFR, CaCO3/CO2 reactors with suitable media, and my DIY two part systems all add magnesium for you, without measurement.

4. It will take a very long time for any sort of significant deviation to show, and if you also do water changes, it likely never will.

To some this will sound like a joke, but I think many reefers, especially newer reefers, would be better served by RMM than testing and retesting, dosing and redosing and then getting a new kit and testing again. Just a few minutes ago I finished a thread where a kit change gave a 200 ppm difference in magnesium.

Just say no. Exact magnesium levels are just not that important.

Thank Poseidon, I was terrified that I was going to have to buy a kit for this. I just got through an ordeal with my API calcium test being wildly inaccurate and I was wondering if I needed to buy a magnesium test too; this answers this question! Thank you for saving me the headache!

 

[visioned]

i've used my hanna mg checker once in about 5 years =]

 

[vahegan]

1 ppm = 1 mg/kg

Since 1 L of seawater weighs about 1.024 kg, they are close, but not identical.

I weighed mine, it was 1.026 kg

I test Mg weekly, along with Ca, PO4, and NO3. Since I got the Hanna checkers and a AutoAqua Smart Stir, this was a breeze. I had to adjust the CaCl2/MgCl2 proportion from 400/150g to 400/100g in my 2-part mix, when my magnesium started to elevate above 1600 (even though I do about 5-8% weekly water changes), therefore I find testing for Mg maybe useful.

 

[Bob Weigant]

I dont even remember the last time I tested for Mag