Magnesium - How low is too low

[Narideth]

Howdy guys.

So I finally got a magnesium test in for my tank so I could check the magnesium levels, particularly since my hammers haven't really been happy in a while. They're extending, but it's not full extension, and I've seen in a half dozen sources that checking magnesium is something to keep in mind for them if they're not fully happy.

Here's my conundrum. My magnesium test came in a 1020 on a salifert testing kit, which right away, is lower than all sources say is good for a reef tank. My question is - my alk and calcium are both steady around 8 for alk and 400 for calcium. Should I attempt to push magnesium higher, or will it throw the others out of balance? This is a little more advanced in reef chemistry than I've gotten so far and mostly what you hear is, don't chase perfect numbers, chase stability.

The tank is 6 months old, not brand new but still in the middle of becoming seasoned. I had a scare with my clownfish over something in the tank causing them serious distress, but they're doing much better now and all of the other corals seem to be opening and happy. The only other LPS I have are blastomussa and goniopora, both fluffy and growing.

Current params:
Evo 13.5 gallon tank
Salinty: 1.025
Temp: 79-80
Alk: 8
Cal: 400
Mg: 1020
PH: 8
Nitrate: 20 ppm
Phos: .01
Ammonia: 0
Nitrite: 0

 

[paragrouper]

Before you dose anything, I recommend you retest. do you do regular water changes? This will usually keep Magnesium in line.

 

[Narideth]

Before you dose anything, I recommend you retest. do you do regular water changes? This will usually keep Magnesium in line.

That was a good suggestion on the retest, but unfortunately it came up with the same numbers.
I do regular water changes, but even above that, the tank water has had 3-4 30% water changes within the last two weeks because of that issue with the clowns I mentioned in the first post. If my mixture was going to maintain magnesium, I would have assumed that many water changes would have it at a suitable level? That's quite a dilution/refreshing amount.
Normally I do 30% water changes about every 2-3 weeks, but I don't have any previous tests to ascertain levels beyond today for magnesium as a baseline. Those changes have maintained all of my other parameters.

Nothing other than unhappy hammers brought me to suspect magnesium, I could let it keep running, test over a couple of weeks and see how magnesium proceeds?

 

[Garf]

Howdy guys.

So I finally got a magnesium test in for my tank so I could check the magnesium levels, particularly since my hammers haven't really been happy in a while. They're extending, but it's not full extension, and I've seen in a half dozen sources that checking magnesium is something to keep in mind for them if they're not fully happy.

Here's my conundrum. My magnesium test came in a 1020 on a salifert testing kit, which right away, is lower than all sources say is good for a reef tank. My question is - my alk and calcium are both steady around 8 for alk and 400 for calcium. Should I attempt to push magnesium higher, or will it throw the others out of balance? This is a little more advanced in reef chemistry than I've gotten so far and mostly what you hear is, don't chase perfect numbers, chase stability.

The tank is 6 months old, not brand new but still in the middle of becoming seasoned. I had a scare with my clownfish over something in the tank causing them serious distress, but they're doing much better now and all of the other corals seem to be opening and happy. The only other LPS I have are blastomussa and goniopora, both fluffy and growing.

Current params:
Evo 13.5 gallon tank
Salinty: 1.025
Temp: 79-80
Alk: 8
Cal: 400
Mg: 1020
PH: 8
Nitrate: 20 ppm
Phos: .01
Ammonia: 0
Nitrite: 0

You using a calibrated salinity tester?

 

[ptrick21186]

What salt are you using? I've been noticing that the Reef Crystals I buy is only coming in at about 1100ppm Mag. I've been having to dose Mag into the new water to get it up to where I like it (1350 target).

 

[Narideth]

I'm using Instant Ocean salt, just the regular kind. My salinity tester was calibrated a bit ago, and I've been meaning to get a backup for the purposes of redundancy, but at this exact moment, I don't have the means to test calibration.

 

[ptrick21186]

I'm using Instant Ocean salt, just the regular kind. My salinity tester was calibrated a bit ago, and I've been meaning to get a backup for the purposes of redundancy, but at this exact moment, I don't have the means to test calibration.

Make some clean saltwater at the level you use and check the mag level on that. I think you'll find it's pretty low

 

[Garf]

I'm using Instant Ocean salt, just the regular kind. My salinity tester was calibrated a bit ago, and I've been meaning to get a backup for the purposes of redundancy, but at this exact moment, I don't have the means to test calibration.

Does the instant ocean salt say that the Alkalinity should be about 8, at full strength 35 ppt water? Lots of folk get salinity wrong, along with magnesium testing.

 

[EeyoreIsMySpiritAnimal]

I'm using Instant Ocean salt, just the regular kind. My salinity tester was calibrated a bit ago, and I've been meaning to get a backup for the purposes of redundancy, but at this exact moment, I don't have the means to test calibration.

Calibrate your salinity tester very frequently... Every water change if possible

 

[Narideth]

Make some clean saltwater at the level you use and check the mag level on that. I think you'll find it's pretty low

You guys are all full of great suggestions. The fresh salt water came in at 990 for magnesium, so something does seem off according to the following information.

The bag itself doesn't say what the alk and magnesium should be, but I have two sources for that as shown below
A website comparing multiple salt mixes:
At 35ppt = 400 calcium, 11 dkh, 1350 magnesium

Another website gives a variable:
1.023 - 1.025 Specific gravity = 8 - 12 dKH, 1250 - 1350 ppm magnesium

I'll get my salinity tester calibrated and come back with updates. Thank you all for giving me a direction to start in!

 

[ptrick21186]

From what I've read magnesium is the more expensive of the elements in synthetic sea salt. It's what separates the high dollar salts from the lower cost stuff. So it's most likely gonna be one of the first elements to be cut when making a salt blend more cost effective. With Reef Crystals coming in about 1100, the 990 from your standard IO salt, I'd have to assume is probably correct.

I'd recommend doing what I do. First SLOWLY dose Mag to get your tank to where you want it. Once that's good I'd measure your clean saltwater for your weekly WCs, and using a calculator from say BRS, dose Mag to get that up to tank level. You'll probably find that will be sufficient to keep your Mag levels where you want it. Magnesium doesn't deplete as fast as Alk and Calcium.

 

[Dennis Cartier]

I respectfully suggest your salinity is way low because there is no way that IO and Reef Crystals would be giving magnesium that low. The salinity being too low is probably what is annoying your hammers.

I suggest getting a TM High Precision Hydrometer to measure your salinity. They don't require any calibration and are essential for cross checking other salinity devices calibration. Just make sure you buy as well, the tall plastic cylinder they sell for it, to make taking measurements easy.

 

[Randy Holmes-Farley Verified Community Expert]

I strongly expect the magnesium test is inaccurate or the salinity is lower than you think. Both errors are very common.

That said, if it really is 1020 ppm, then raising the salinity to 35 ppt (sg = 1.0264) from a sg of 1.025 will boost that to 1077 ppm.

As to the title question, I'd advise folks to keep magnesium to at least 1250 ppm.

 

[Narideth]

Update: So, now the mystery grows. Having acquired calibration fluid and tested my refractometer three times - twice with the solution and once with RO/DI just for kicks - each one indicates that my refractometer was almost perfect and not at all seriously out of calibration like I thought might be the case. It was at most, a single point of salinity off, as in 36 ppt rather then 35 ppt.

So.. where do I go from here? Salinity seems good, the question of magnesium remains.

 

[Randy Holmes-Farley Verified Community Expert]

Update: So, now the mystery grows. Having acquired calibration fluid and tested my refractometer three times - twice with the solution and once with RO/DI just for kicks - each one indicates that my refractometer was almost perfect and not at all seriously out of calibration like I thought might be the case. It was at most, a single point of salinity off, as in 36 ppt rather then 35 ppt.

So.. where do I go from here? Salinity seems good, the question of magnesium remains.

How did you make the new salt water to test? Sometimes buckets are in homogeneous.

That said, an off batch of salt is unusual and a bad mag test result is not.

I’d double check the magnesium testing somehow.

 

[ptrick21186]

I'm gonna double check my reef crystals. I'm pretty sure it was 1100 but now you guys got me second guessing lol

 

[Randy Holmes-Farley Verified Community Expert]

I'm gonna double check my reef crystals. I'm pretty sure it was 1100 but now you guys got me second guessing lol

Yes, double check it with a different test kit, preferably.

 

[srobertb]

Take it to a LFS or ask on FB (or wherever local reefers dwell) if someone can test for you. Have someone else test your water.

 

[Pistondog]

Update: So, now the mystery grows. Having acquired calibration fluid and tested my refractometer three times - twice with the solution and once with RO/DI just for kicks - each one indicates that my refractometer was almost perfect and not at all seriously out of calibration like I thought might be the case. It was at most, a single point of salinity off, as in 36 ppt rather then 35 ppt.

So.. where do I go from here? Salinity seems good, the question of magnesium remains.

If you need a 2nd mag test kit, i just got the aquaforest one, cheap and easy.
Fwiw, my expired red sea kit read 20% low.

 

[Narideth]

Alright, another update. This one is rather sad. I lost my clownfish in this tank, though I don't know if it's related or if it just made them a bit weaker so something else could claim them.

That being said, I took my water to be tested at two different LFS, one which I trust as a huge coral provider and the other, Petco. I went in for a magnesium check, but when the numbers came back with what I would have expected from my attempts to slowly raise salinity due to my refractometer being 'slightly' out, I asked them to test salinity on a whim.

LFS: Magnesium 1120, Salinity 1.020
Petco: Salinity 1.019

I've bumped the salinity up by .002 over the last week, which means it could have been as low as 1.017. Yikes, no wonder my corals are unhappy.

Both used refractometers, the LFS calibrated right there in front of me. My refractometer or the calibration solution are totally busted. I'm ordering a new one. I got a swing arm at petco, the fluval one in attempt to set up the right salinity and get that going while I wait for the new refractometer, but the thing reads the same water as 1.023! I'm trusting the two separate refractometer readings, but that means this dang fluval hydrometer will need to be returned too I guess. Is it common for swing arm hydrometers to be that far out of calibration?

Thanks to those who mentioned salinity, it got me thinking about it when I went to get my magnesium tested. The process continues, but ironically enough, my magnesium was correct and salinity was off.