Magnesium test kits

[mojo]

I've got a bit of a dilemma with my magnesium testing.

I've been using a Seachem Reefstatus Magnesium test kit for about a year. It's the one that comes in the white plastic box, and involves adding the cotton ball to separate the interference ions, etc.

The other day I picked up a Salifert Mg test kit in an attempt to make testing magnesium easier. However, my test results are WAY different.

Same water, tests taken minutes apart. I did two tests with each kit (it was a fun evening...). I was very careful to follow the test procedure to the letter:

Salifert test #1: 1770ppm
Salifert test #2: 1710ppm

Seachem test #1: 1450ppm
Seachem test #2: 1425ppm

At least I'm consistent, but which one is right? 300ppm is a pretty serious difference...

Well, my Seachem kit comes with a 1100ppm reference sample that I've never opened. I broke the seal and ran both test kits against it:

Salifert reference test: 1500
Seachem reference test: 1150

Woah. I still tend to believe that the Seachem is a better kit, but which one can I trust? If I assume that the scales are linear and the Salifert is off by +400 (read 1500 from a 1100 reference) and the Seachem is off by +50 (1150-1100), then we get the adjusted test results:

Salifert test #1 adjusted: 1370ppm
Salifert test #2 adjusted: 1310ppm

Seachem test #1 adjusted: 1400ppm
Seachem test #2 adjusted: 1375ppm

But the big question is - can I normalize like that? More importantly, which one should I use? You can argue that stability is more critical with temperature, pH, salinity and some others, but I need to know what my Mg is - at least with 100ppm.

Any ideas?

 

[chemically_balanced]

How about I let you barrow my Seachem kit and you test with it...

 

[sailfish]

I used to use salifert then one day I bought a elos one and realized I had a mag problem. I can't remember how far off it was but I know it was significant.

Joe

 

[derek_s]

THat is a pretty advanced question, and I'm wondering if you might need to reach salifert or seachem and see. I'm not sure if you could just subtract the difference, or if it operates more on a function curve type thingie.

 

[ralph atl]

screw salifert! THEY almost pushed me over the edge & out of the hobby! ELOS!

 

[ralph atl]

I wouldn't trust either one!

 

[mojo]

Chemically_Balanced;273641 wrote: How about I let you barrow my Seachem kit and you test with it...

It'd certainly help to have yet another data point...

sailfish;273647 wrote: I used to use salifert then one day I bought a elos one and realized I had a mag problem. I can't remember how far off it was but I know it was significant.

But how do you know that the Elos is right and not the salifert?

Derek_S;273656 wrote: THat is a pretty advanced question, and I'm wondering if you might need to reach salifert or seachem and see. I'm not sure if you could just subtract the difference, or if it operates more on a function curve type thingie.

I'm not sure either. I may end up posting this one in the Reef Central chemistry forum....

 

[ralph atl]

just buy an ELOS kit and be done with it.


This kinda crap will drive you crazy as it did me about 18 months ago when HABIB was run out of reefcentral because of his alk kits.

 

[ralph atl]

The salifert kit that I happened to use before I gave it away, was 100 points lower than actual. That was surprising.

 

[mojo]

mysterybox;273670 wrote: The salifert kit that I happened to use before I gave it away, was 100 points lower than actual. That was surprising.

But what is "actual" and how do you determine that?

 

[derek_s]

mojo;273664 wrote:
But how do you know that the Elos is right and not the salifert?

I agree here. How do we ever know?

But I would lean towards the reading that most accuratly resembles the reference fluid. Maybe you could even source some additional ref fluids to test and be sure?

 

[mojo]

Derek_S;273673 wrote: Maybe you could even source some additional ref fluids to test and be sure?

Either that or make my own reference fluid. IE- add a certain amount of MgCl to a certain amount of RODI water. That's probably about the closest you'd be able to get, and should be fairly easy to find the proportions...

 

[steve]

I think that would be the best bet, because you calling Salifert or Seachem would be a waste of time because obviously the person on the other end of the line would obviously side with the company that employs him/her.

 

[sailfish]

I tested the elos against a reference sample I had left from a seachem test and it was right on. Only thing is my test was the old one that only gives reading in 100s. The reference read 1160ppm. If you are interested I can test my current test but it's still the old style that gives reading in the 100s. I am not one to run around promoting a product but I would say you should give them a try. If I were you I would bring in a sample to Chris at Einstein and have him test it for you then compare and decide if you want to buy one.

I suck at chemistry so I can not help with you question except to say I would use the one that is more accurate. I would also return the one I bought.

Joe

 

[sailfish]

If you want I have aonther referance sample that has never been used made by fauna marin you can have.

Joe

 

[mojo]

Thanks for the offer, although I'm afraid to trust any reference sample at this point. I think I'm going to have to make my own...

 

[patrick214]

If it helps any, I used to use seachem for Mg testing and it would always read between 1100-1150. Now I have both an Elos and Salifert test that have always read between 1400-1450 everytime. The same seachem mg test still reads 1100 when i've tested it against elos and salifert. Honestly, Im not a big fan of the Seachem test kits. I've found that they register significant lower than all my other test kits across the board. I trust the elos or salifert kits over my seachem any day.

 

[derek_s]

Wierd, my seachem always seems to read 1100, all the time. Over time I put in about 2 lbs of MgCl and it still reads about the same. I wonder if I am experiencing the same phenomena?

 

[thewarbrd]

I know we have a UGA student or three around here but I don't know their majors. I work at UGA two buildings over from the chemistry department. I could contact them to see if they have any bored student that could provide either a reference solution (which reading around the net after seeing this thread, someone claims that the seachem reference solutions are actually certified by UGA) or some other means to compare a few of our kits with.

I take everything with a grain of salt when it comes to test kits and for things like PH I look just want to make sure things are constant more than anything. But I just picked up a salifert Mg kit last week and now I'm curious that my readings of 1125-1150 are up to 400pts off...

So without 3-4 kits from any one brand from different reagent batches, how would we know that if one persons kit tests high, another isn't testing low. Or all the kits are dead on like ELOS's 'NIST validation' is supposed to claim makes them all identical vs 'Joes random watercolor mixing test kit reagent batch of the week'?

 

[mojo]

thewarbrd;273767 wrote: (which reading around the net after seeing this thread, someone claims that the seachem reference solutions are actually certified by UGA) or some other means to compare a few of our kits with.

You realize you're talking to a GT alum, right? "Certified by UGA" won't end well when the jokes start flying... :lol2:

Seriously, making up a solution of MgCl in RODI water can't be all that hard - measure by weight, add to the RODI, and you have a known amount. I'm posting on RC today to see if RHF has any insight.