Low Magnesium!

[FUNGI]

120G Mixed Reef (heavy on softies).
Tank History: Has always been on the low side for MG (mean: 1200)
Dosing Mg: 25ml Red Sea daily.
Dosing Kalk every other day (drip does at night)
Dosing NoPox: 5ml eveyday
Last test (Last night). Confirmed at home with Hanna, but went to LFS to double check:
Mg at 975....? Its never dropped that low
Cal. 470
dKH: 8.2
NO3: 20
NO2:0
NH3:0
Anyone have any ideas on the depletion of the Mg?

Duncans starting to show signs of stress /tissue receding, (maybe a different issue)
No other signs from any other corals......

NOTE: I buy NSW from LFS. Water changes every 6~7 months......

 

[Randy Holmes-Farley Verified Community Expert]

Is it really Natural seawater? What salinity? Try your kit on that, if you have any.

Magnesium kits are notoriously inaccurate. 975 ppm in a soft coral tank seems likely a test error.

Which is why I recommend not testing it:

https://www.reef2reef.com/threads/just-say-no-to-magnesium-testing-rmm-is-born.1017528/

 

[Uncle99]

120G Mixed Reef (heavy on softies).
Tank History: Has always been on the low side for MG (mean: 1200)
Dosing Mg: 25ml Red Sea daily.
Dosing Kalk every other day (drip does at night)
Dosing NoPox: 5ml eveyday
Last test (Last night). Confirmed at home with Hanna, but went to LFS to double check:
Mg at 975....? Its never dropped that low
Cal. 470
dKH: 8.2
NO3: 20
NO2:0
NH3:0
Anyone have any ideas on the depletion of the Mg?

Duncans starting to show signs of stress /tissue receding, (maybe a different issue)
No other signs from any other corals......

NOTE: I buy NSW from LFS. Water changes every 6~7 months......

I only need 5ml per day of Red Sea MG to maintain 1400ppm in 250G heavy stocked SPS and clams, so if anything, you may be much, much higher 975ppm.

I can see using a lot of product to raises, but once there 1/6th of Alk is plenty in most cases.

Check that number with another kit.

 

[FUNGI]

Hi Randy,
Salinity at 1.024
I did a Hanna test at home, and got the low Mg, which prompted me to get a second opinion at LFS...same results.
I have a feeling its the NSW from them.....( I did a 30% WC 2 weeks ago)......

 

[FUNGI]

Salinity was via refractometer at home and then same at LSW.....

 

[FUNGI]

Is it really Natural seawater? What salinity? Try your kit on that, if you have any.

Magnesium kits are notoriously inaccurate. 975 ppm in a soft coral tank seems likely a test error.

Which is why I recommend not testing it:

https://www.reef2reef.com/threads/just-say-no-to-magnesium-testing-rmm-is-born.1017528/

Read it 3 or 4 times already....maybe a 5th time is a charm LOL.....

 

[Randy Holmes-Farley Verified Community Expert]

Hi Randy,
Salinity at 1.024
I did a Hanna test at home, and got the low Mg, which prompted me to get a second opinion at LFS...same results.
I have a feeling its the NSW from them.....( I did a 30% WC 2 weeks ago)......

Natural seawater at sg= 1.024 should have 1164 ppm magnesium.

 

[FUNGI]

Natural seawater at sg= 1.024 should have 1164 ppm magnesium.

100% agree.....investigating some more.

 

[PharmrJohn]

Natural seawater at sg= 1.024 should have 1164 ppm magnesium.

Dude. Do you know these numbers pretty much off the top of your head? This is not a challenge post. I'm just amazed at your knowledge base. I seriously want to know what you know.

 

[Miami Reef]

Dude. Do you know these numbers pretty much off the top of your head? This is not a challenge post. I'm just amazed at your knowledge base. I seriously want to know what you know.

Also curious if he knows the answer based on memory or if he used a calculator?

 

[FUNGI]

Dude. Do you know these numbers pretty much off the top of your head? This is not a challenge post. I'm just amazed at your knowledge base. I seriously want to know what you know.

He has a talent!
His Title does say Reef Chemist.......

 

[PharmrJohn]

Also curious if he knows the answer based on memory or if he used a calculator?

It's always possible, and I did consider it. But he's GOTTA have a ballpark figure that's plus or minus 5% tops.

 

[FUNGI]

It's always possible, and I did consider it. But he's GOTTA have a ballpark figure that's plus or minus 5% tops.

In the old days, I could reverse cost a Plush toy or Action Figure to within .05cents factory cost.....but thats another time...before my Mg worries...LOL

 

[Randy Holmes-Farley Verified Community Expert]

lol

Phone calculator
35 ppt (sg = 1.0264) seawater always has 1280 ppm magnesium

Ratio of sg tank water to sg of 35 ppt seawater will give ratio of magnesium

24/26.4 times the NSW mag at 35 ppt = 0.909 x 1280 = 1164 ppm. :)

 

[Miami Reef]

lol

Phone calculator
35 ppt (sg = 1.0264) seawater always has 1280 ppm magnesium

Ratio of sg tank water to sg of 35 ppt seawater will give ratio of magnesium

24/26.4 times the NSW mag at 35 ppt = 0.909 x 1280 = 1164 ppm. :)

Hey, so how did you know to make 1.024 as “24?” and 1.0264 as 26.4?

I tried dividing 1.024 by 1.0264 and then multiplying that by 1280, but I got a different answer (1277ppm)

 

[Randy Holmes-Farley Verified Community Expert]

Hey, so how did you know to make 1.024 as “24?” and 1.0264 as 26.4?

I tried dividing 1.024 by 1.0264 and then multiplying that by 1280, but I got a different answer (1277ppm)

You have to ignore the leading “1”. It boils down to the fact that sg is linear in salinity (ppt). Basically, it is interpolating between sg = 1.000 at 0 ppt and sg = 1.0264 at 35 ppt.

I could post a more complicated formula, but all major ions in seawater can be determined by dropping the one, figure the ratio, and multiply by the 35 ppt value.

For example, ro/di has sg = 1.000.

Ratio is 0/26.4 = 0

So all values are zero.

 

[Miami Reef]

You have to ignore the leading “1”. It boils down to the fact that sg is linear in salinity (ppt). Basically, it is interpolating between sg = 1.000 at 0 ppt and sg = 1.0264 at 35 ppt.

I could post a more complicated formula, but all major ions in seawater can be determined by dropping the one, figure the ratio, and multiply by the 35 ppt value.

For example, ro/di has sg = 1.000.

Ratio is 0/26.4 = 0

So all values are zero.

Thank you SO much! I really appreciate it!!