Magnesium

[domination2580]

Hey, I have been testing my tank at 1500 mag using af reef salt. I sent salt to them for testing and icp from them says it's 1350. That's at 33 ppt. I use 1.026, is that that big of a spread for magnesium? And can icp be wrong?

 

[saltyfilmfolks]

Magnesium seems to be the most commonly prone to testing error across the board.

 

[domination2580]

Magnesium seems to be the most commonly prone to testing error across the board.

Agreed but that is a huge difference from icp to test kits.

 

[saltyfilmfolks]

Agreed but that is a huge difference from icp to test kits.

Yes. Yes it is. And seemingly normal.
are you using the red sea test?

 

[domination2580]

Red sea and two different salifert test

 

[saltyfilmfolks]

Wow. thats weird.

 

[redfishbluefish]

If I understand the OP correctly, you state that the ICP was at 33 ppt salinity with a 1350 magnesium level. However, your tank is at 35 ppt salinity. Without taking out a calculator, that would put magnesium up into the 1400's somewhere....not far from where you're testing....and likely within error of the test methods.

 

[Anirban]

If I understand the OP correctly, you state that the ICP was at 33 ppt salinity with a 1350 magnesium level. However, your tank is at 35 ppt salinity. Without taking out a calculator, that would put magnesium up into the 1400's somewhere....not far from where you're testing....and likely within error of the test methods.

Yes, thats correct. It should be somewhere near 1430ppm with 35 ppt salinity.

 

[domination2580]

Sorry. That's where i keep my Dt. I tested the frag tank which I confirmed and calibrated it's at 33ppt.

 

[chipmunkofdoom2]

You keep your salinity higher than they tested, so you need to adjust for that. If you keep your tank around 35ppt and they tested the water around 33ppt, that means your tank has about 6% more mineral content then their test did (35ppt / 33ppt = 106%). If you multiply their magnesium value by around 1.06 to adjust for this difference, you'd get around 1,430 ppm Mg (1,350ppm Mg * 1.06 = 1,431ppm Mg). So basically their results say your Mg level should be around 1,430ppm when your tests say it's around 1,500ppm. That's less than 5% error ((1,500ppm - 1,431ppm) / 1,500ppm = 4.6%). That's not too far off.

I'd also check your refractometer's calibration. If your salinity is a little high, that could explain the difference as well. Your refractometer may tell you your saltwater is 35ppt, but it may in fact be higher, which would mean the magnesium level makes even more sense.

Sounds like you should stop dosing Mg if you are currently. Or switch to a salt mix with lower Mg if you aren't dosing.

EDIT: Just read your reply. So your frag tank, which is around 33ppt salinity, test 1,500ppm Mg?

 

[domination2580]

You keep your salinity higher than they tested, so you need to adjust for that. If you keep your tank around 35ppt and they tested the water around 33ppt, that means your tank has about 6% more mineral content then their test did (35ppt / 33ppt = 106%). If you multiply their magnesium value by around 1.06 to adjust for this difference, you'd get around 1,430 ppm Mg (1,350ppm Mg * 1.06 = 1,431ppm Mg). So basically their results say your Mg level should be around 1,430ppm when your tests say it's around 1,500ppm. That's less than 5% error ((1,500ppm - 1,431ppm) / 1,500ppm = 4.6%). That's not too far off.

I'd also check your refractometer's calibration. If your salinity is a little high, that could explain the difference as well. Your refractometer may tell you your saltwater is 35ppt, but it may in fact be higher, which would mean the magnesium level makes even more sense.

Sounds like you should stop dosing Mg if you are currently. Or switch to a salt mix with lower Mg if you aren't dosing.

EDIT: Just read your reply. So your frag tank, which is around 33ppt salinity, test 1,500ppm Mg?

The water i tested is at 33ppt after calibration of my refractometer.

 

[domination2580]

So here are the results on my icp.
Salinity is 34ppt. Which is only 1 off of 33ppt. So how does 1 less ppt make it 1500?

 

[domination2580]

Anyone?

 

[chipmunkofdoom2]

The 34ppt of the test and the 33ppt of the frag tank do make things a bit less clear cut. I suppose it is possible for ICP testing to be "off", but I would sooner blame a bad batch of test kits or testing procedure rather than the ICP testing. I would put more faith in laboratory equipment than $15 test kits which rely on the human eye for color-based titration. But, even lab equipment can be wrong.

Regardless, 1,500ppm is high, but it's only about 10% higher than the 1,350ppm many people strive to maintain. Personally, I wouldn't treat this as an emergency, but I would probably switch salt mixes. The reviews on BRS complain of high Mg levels and batch consistencies with AF Reef Salt. By performing water changes with water that contains less Mg than your tank, you will effectively lower the Mg over time.

 

[domination2580]

See the thing is, I have a tested 3 times using red sea, and then tested two more times with 2 different salifert test kits. I have also used a friend's red sea test kit as well to verify.

 

[Scott.h]

See the thing is, I have a tested 3 times using red sea, and then tested two more times with 2 different salifert test kits. I have also used a friend's red sea test kit as well to verify.

Either way, test kit error or not I'd keep doing what you're doing. I'd trust icp. 1350 is a little higher than what I aim for, but right where you should be. I'd get your po4 up a tad, stop with gfo for a bit and keep going. With your aluminum elevated are you by chance using marine pure media? If so how old is it?

 

[Lance M.]

It probably has to do with % error from your handheld refractometer, test kit, icp, etc.

For ICP analysis, your sample is diluted prior to testing. I dont know what procedure they or anyone else uses. So for instance, just as an example, the sample is diluted to 10%, the reading on the ICP for magnesium could be something like 135, then you multiply by 10, send result 1350ppm magnesium. If this 135 reading was obtained via radial view then there could easily be a 5% error giving a range 128-142 or 1280 to 1420ppm final result.

Thats just hypothetical. I dont what they actually do when they test.

Error could also just come from sample handling, calibration curve, instrument, etc.

 

[domination2580]

Either way, test kit error or not I'd keep doing what you're doing. I'd trust icp. 1350 is a little higher than what I aim for, but right where you should be. I'd get your po4 up a tad, stop with gfo for a bit and keep going. With your aluminum elevated are you by chance using marine pure media? If so how old is it?

This was fresh made salt water. Not out of tank. Lol

 

[domination2580]

Ok let me clarify. I don't know why I put what i did from the start. I sent salt to them, they mixed it to 34ppt, and got 1350 pin the newly made salt water. I tested my frag tank I just got up and running at 33 ppt and it's reading 1580 now... So idk what the real mag is. I'll be buying af test kit and checking with that. If it turns out correct then I know I can rust the af test kits

 

[Scott.h]

The problem with testing new saltwater is every bucket is going to change with all parameters to some extent. That holds true to every brand I've tried. I wonder if you let someone else test the water if they'd test the same results.