3 magnesium tests reading different results

[Marc2952]

Today i tested my two old salifert magnesium test kits with the new ones since ive noticed sometimes its off and to my surprise the difference is substantial. How can i know which one is correct?
Test kit 1: 1490
Test kit 2: 1440
Test kit 3( this is the old one ive been using) 1310
I was planning on doing an icp test to see which one is closest to their results.

 

[fishface NJ]

did the two old test kits expire?

 

[Marc2952]

did the two old test kits expire?

Nah they all expire in 2023, the two old ones read 1440 and 1310, the new one reads 1490 lol i dont know which ones is right.

 

[fishface NJ]

Mag tests are not as accurate. What are your Kh and Ca?

 

[Marc2952]

Mag tests are not as accurate. What are your Kh and Ca?

Currently cal 450 and alk 8.6

 

[josephxsxn]

Average the results?

 

[reefiniteasy]

OMG! I dealt with this today. I test Mg once a week post water change. Last week I did my tank transfer and tested all parameters when I was done. Mg was 1380ppm as tested using the last bit of my current Salifert Mg test kit. Today I checked all parameters, using a new Salifert Mg kit and the tank measured 1500. Like what the heck. All parameters are perfect and stable and the tank looks great so I’m not worried. But still. I can’t explain it. I dose ESV 2-part in equal amounts and I know the calcium component contains magnesium, but I didn’t think it was enough to cause a 1500ppm spike.


Alk - 7.6dKH dose 4.4ml
Mg - 1500
Ca - 450ppm
PO4 - .01ppm
NO3 - 2.5ppm

 

[Fishingandreefing]

Adding 3 up and divided by 3, maybe lol. I had my friend tested my mag by the Red Sea and it was consistent with my two years expired kit. Not sure if the Red Sea was accurate to begin with.

 

[Marc2952]

Average the results?

But which one is right or closest to the real result? Lol

 

[Marc2952]

OMG! I dealt with this today. I test Mg once a week post water change. Last week I did my tank transfer and tested all parameters when I was done. Mg was 1380ppm as tested using the last bit of my current Salifert Mg test kit. Today I checked all parameters, using a new Salifert Mg kit and the tank measured 1500. Like what the heck. All parameters are perfect and stable and the tank looks great so I’m not worried. But still. I can’t explain it. I dose ESV 2-part in equal amounts and I know the calcium component contains magnesium, but I didn’t think it was enough to cause a 1500ppm spike.


Alk - 7.6dKH dose 4.4ml
Mg - 1500
Ca - 450ppm
PO4 - .01ppm
NO3 - 2.5ppm

Did you double check? Has to be a test kit error, ive noticed salifert test kits arent too accurate, i had an issue with the calcium one too. I think i will just test all 3 the day i take the water sample for the icp test and see which one is right.

 

[josephxsxn]

But which one is right or closest to the real result? Lol

Even the ICP test is going to have a range of accuracy and precision. Also I would giggle if you get a split result between two with ICP. I totally get the desire to want to be spot on.. But as many people here will tell you it's about stability, pick one test that's repeatable for you and get it to your target value and hold it there. BRS recommends the aquaforest mg test because it comes with a correction for calcium.

 

[reefiniteasy]

Did you double check? Has to be a test kit error, ive noticed salifert test kits arent too accurate, i had an issue with the calcium one too. I think i will just test all 3 the day i take the water sample for the icp test and see which one is right.

Did the test twice. Same result, 1485 and 1500. I have another unopened kit. I’ll do it with that kit tomorrow. Tank looks great so I don’t really care all that much, but it is mind boggling.

 

[Reef and Dive]

All those tests are ok for the margin of error they have and do not point to problems. I would not worry (but I personally prefer to keep Mg around 1150-1300).