Salifert v. Seachem Ca Test Results

[Habib]

Habib,

Thank you for taking the time to try and explain the deviation. ........
...........

Thanks!

Habib,

What would explain the Seachem standard giving their test kit the same results; the LaMotte Test kit the same results; but the Salifert kit 25% higher results?

Should not a standard, regardless of 'systemic' issues give the expected results? Many of the examples you give is measuring the unknowns and measuring against Salifer internal standards. What do the Salifer internal standards read on the LaMotte and Seachem test kits?

I still have a concern when my LaMotte Test Kit reports X Ca; my Seachem TK reports X Ca; and the Salifert TK reports X + .25X Ca. The color change with the Seachem TK is very clear. Enough so that I can tip-off partial drops and see a change.

Thank you. Hope you had a good vacation!

Perhaps the Seachem is adjusted to their reference or the reference value is adjusted to their kit or perhaps another scenario? Hard to say.


I still have a concern when my LaMotte Test Kit reports X Ca; my Seachem TK reports X Ca;

I don't have experience with the Lamotte (and also not with the current Seachem version). However, I explained in my previous post that the Lamotte requires a 12.9 fold dilution with DI water. A slightly premature end-point by 8 ppm will give a 12.9 x 8 = 103 ppm too low value.

When we use various standards and also various natural seawater samples (for which the salinities and calcium are known) we get the correct value with the Salifert.

Should not a standard, regardless of 'systemic' issues give the expected results?

We don't know in what matrix the Seachem "standard" is and also not how the documented value was obtained and what the error in that value is.

 

[Habib]

I've never done such tests because I am not convinced that the results of such tests reflect on the ability of the kit to work in seawater.

Several commercial standards made in freshwater contain acid and even besides that, the Salifert will be able to measure high calcium values in freshwater accurately if the procedure is modified. This suggests that using standards in a freshwater matrix can be tricky.

 

[Habib]

Unless there is inflow of freshwater the calcium value for natural seawater are accurately known as a function of salinity.

Here is a post of a year ago and suggests that the Salifert he used certainly does not give results higher by 25% then actual. Perhaps, in his case, even slightly lower than actual.

I collected water samples from different seas and measured Ca with Salifert Ca test and there are results:

Mediterian, Adriatic Sea, Pag , Novalja salinity 3,8 % , Ca = 435ppm
Red Sea, Sinai, Shark Bay , salinity 4,1 % , Ca = 450 ppm
IndoPacific, Indonesia, Bali, Kuta Beach, salinity 3,5 % , Ca = 345 ppm

It is very confusing that Ca level in the Bali Sea is only 345 ppm.

Acctually I believe in Salifert test, because all readings are logical, only Ca level in Bali sea is lower than my expectance.

I also check with JBL test kit and the readings are similar, Unfortunately JBT test resolution is only 20 ppm.




KH is everywhere between 7 and 8

The full thread is there:
http://www.reefcentral.com/forums/s...id=3345247&highlight=red+ANd+bali#post3345247

 

[Habib]

Habib,
.............................

Can the reference be such that it only works or matches a specific brand of test kit.? Somewhere in this thread I posted where I tested the SeaChem reference with the Salifert and it was around 500??

..............

Perhaps the reference might be such but the values for the same marine water sample also don't match.

Your post, Mark Middleton's , Leebeca's and a few others made me believe that the 25% or so difference might be systematic.

 

[leebca]

I've never done such tests because I am not convinced that the results of such tests reflect on the ability of the kit to work in seawater.

But we're not suggesting to test the kit's ability to test seawater. Just the kits ability to do so reliably and accurately.

 

[leebca]

Habib,

The "system issue" is unclear to me. Sorry.

I don't have experience with the LaMotte (and also not with the current Seachem version). However, I explained in my previous post that the LaMotte requires a 12.9 fold dilution with DI water. A slightly premature end-point by 8 ppm will give a 12.9 x 8 = 103 ppm too low value.

Isn't this the ability of the operator to find the correct endpoint? and to make the correct dilution? Isn't this reflected in the reproducibility or the precision of the results? If I do multiple tests (e.g., 5 tests), aren't these variables taken into account in the spread of the data/results?

How would you eliminate this systemic concern?

I appreciate the testimonial, but it's easy to match each one you provide with a counter-testimonial. There are many variables, time, changes in test reagents, was he using kits he bought from a dealer, etc., etc. I'd suggest we stick to the science and clear that up first.

Your post, Mark Middleton's , Leebeca's and a few others made me believe that the 25% or so difference might be systematic.

Does this mean that two test kits may have a systemic problem, but each has a different systemic problem (Seachem because it matches the reference; LaMotte because there's a dilution)? Should we test other kits on the reference and seawater, or if the results are the same, are they also afflicted? I have a Hagen Ca test kit, too. There is no dilution with it; it is a titration test. I'll post my results with it, shortly on the SeaChem reference.

Thanks for your input!

 

[leebca]

I performed a Hagen Test (one).

The end point was between 21 and 22 drops. That calculates to approx. 430 ppm Ca.

The SeaChem reference is 390 ppm.

 

[leebca]

Just checked previous posts. I guess I've done this test before.

The 5. ml mark on the Hagen test tube shows the meniscus touching the bottom of the line with adding 5.00 ml of distilled water, with a Class A vol pipet.

If the sample is plus or minus 2 drops (generous) then the sample varies by +- 0.1 ml or 1/50 or 2%

The endpoint is readable to the the size of the drop of the dispensing bottle. Using a standard 0.05 ml for that error and it factors 20 ppm into the error of the titration. Add to this the error of the operator determining the endpoint. I don't know if the indicator takes up/uses any of the titrant in their kit.

If all were shifted to one end of their ranges, we might be in the neighborhood of about a variation of 30 ppm PLUS the error of determining the endpoint (should be less than a whole drop, maybe 10 ppm). But this 'systemic' variation can be estimated by running multiple test. I don't call this a "systemic" issue, but a precision issue. But then, as I noted above, the use of 'systemic' isn't completely clear to me.

 

[RichardS]

Are you basing all of this off only one Salifert kit? Just wondering if perhaps your kit is bad for whatever reason.

I currently use salifert both at my store and at home but used seachem's kits prior to switching. When I checked the kits (both at my store and at home, different kits) against each other I saw no major deviation between the two. That was about a year ago so I don't know the exact numbers.

 

[MiddletonMark]

Habib -

I guess I'm on the fence. The only thing I've recently compared my Seachem Ca test was two Salifert kits of similar origin.

I've not run another comparison [yet], nor tested the reference recently.

I had assumed that my test kit must be `wrong', `old', or `contaminated' when comparing to the Salifert tests - not because I believe the components have changed or the test truly is the above.

But when comparing very different #'s, I tried to find some reason and assumed that there was a problem with the kit.

If Leebca and any others have similar results - then I think my assumption of a bad kit was incorrect. Maybe my test is more correct than my buddy's Salifert .... now I just don't know.

When it was my kit, alone, then I made a guess. Now, I just wonder.

And I probably always will, as my kit has all of 15 tests left probably. Provided my Ca doesn't go wildly up/down, in the end I don't really care much if it's 375, 425, or 475. All are fine in my mind.

 

[RichardS]

Habib -
Provided my Ca doesn't go wildly up/down, in the end I don't really care much if it's 375, 425, or 475. All are fine in my mind.

There's no magic number. Stability is always more important.

 

[steve the plumb]

but wich test kit kit is the closest to being accurate if that is at all possible.Why is it that my saliferts has a 100 ppm differance than my seachem.I just went and tested my friends cal level and got 700 ppm from the salifert test .Is this possible?I did the test twice.I did not test with my seachem as I do with when I test my water.I don't understand why the 100 ppm dif between the two..I try to take the air bubbles out and I always follow directions to make sure that no mistakes are made.I tested my water salifert 560 ppm seachem 465 ppm.Could it be the ro water causes the kit to test low?Very frustrating

 

[RichardS]

With the Seachem kit you should be using DI water (TDS = 0). Your RO water could be causing an inaccurate reading.

700 ppm is very unlikely - if even possible. I've only heard of those kind of numbers from people using Oceanic salt.

 

[Habib]

Hobster:

For that Salifert batch when retesting today an archived sample I found when using a commercial calcium in freshwater standard 425 mg/L (should have been 434 mg/L).

Using a natural seawater with a salinity of 36.5 S I found 435 mg/L (should have been 440 mg/L).

The archived sample of that batch performed very good.


Details can be found here below.

1] Used a commercial standard see attachment at end of this post having a specified batch analysis of 1001 +/- 2 mg/L and a density of 1.01 kg/L.

Took 0.876 g which equals to 0.867 ml (weight / density).
The Salifert method is based on a sample of 2 ml so the expected calcium value is: 0.867 / 2 * 1001 = 434 mg/L

Found using your batch 425 mg/L.


2] Used a natural seawater collected off the coast of Lanzarote, a few hundred miles to the west of the Sahara and no inflow of freshwater). Salinity 36.5 S.
Natural sewater with a salinity of 35S has a calcium concentration of 413 mg/Kg = 423 mg/L. A natural seawater with a salinity of 36.5 should have 440 mg/L calcium.

Used 2 ml of the NSW with a salinity of 36.5 and also weighed as a double check the 2 ml sample and found to be 2.044 g.

That sample gave a value of 435 mg/L.

OK, FWIW, I did some tests the morning.

SG 1.025
Mg 1380 Salifert

Alk 2.98 meq/l Salifert

Ca 400 Salifert low res
Ca 420 Salifert high res

(batch 0502C, 0504B, 0503A) purchased 7/05

Ca 350 Seachem ( did twice)
Ca of Seachem reference 400 = 400.
Unknown date of kit 1 yr plus.

A Salifert test of the Seachem Ca reference was 500 so do not know if they are not compatable or this means something?

So based on this my Ca is somewhere between 350 and 420

I would have to lean towards the SeaChem results only because the reference agreed and not having a reference for Salifert. This assumes (as Randy noted) that the referece is also correct.

"So who ya gonna call"?

 

[MiddletonMark]

There's no magic number. Stability is always more important.

Exactly, the one reason why I'm not stressing it much

If it was Alkalinity ... I'd be much more concerned.

 

[Hobster]

Hobster:

For that Salifert batch when retesting today an archived sample I found when using a commercial calcium in freshwater standard 425 mg/L (should have been 434 mg/L).

Using a natural seawater with a salinity of 36.5 S I found 435 mg/L (should have been 440 mg/L).

The archived sample of that batch performed very good.


Details can be found here below.

1] Used a commercial standard see attachment at end of this post having a specified batch analysis of 1001 +/- 2 mg/L and a density of 1.01 kg/L.

Took 0.876 g which equals to 0.867 ml (weight / density).
The Salifert method is based on a sample of 2 ml so the expected calcium value is: 0.867 / 2 * 1001 = 434 mg/L

Found using your batch 425 mg/L.


2] Used a natural seawater collected off the coast of Lanzarote, a few hundred miles to the west of the Sahara and no inflow of freshwater). Salinity 36.5 S.
Natural sewater with a salinity of 35S has a calcium concentration of 413 mg/Kg = 423 mg/L. A natural seawater with a salinity of 36.5 should have 440 mg/L calcium.

Used 2 ml of the NSW with a salinity of 36.5 and also weighed as a double check the 2 ml sample and found to be 2.044 g.

That sample gave a value of 435 mg/L.

Habib,

Thank you for checking that batch number. So based on these results the kit is accurate to +/- 5-9 mg/l ??

Works for me! Closer than I will ever measure

Thanks.:thumbsup:

 

[Habib]

Re: Salifert v. Seachem Ca Test Results

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Each time the Salifert test results is 100 ppm higher than the Seachem (350 v. 250). Seachem results on freshly prepared salt water (from mix) is also different by about 100 ppm. Hard to believe that new salt would have that low of calcium at 1.025 sp. gr. and 75F.
..................

Leebeca, which brand of salt did you test which gave 250 ppm with the Seachem and 350 ppm with the Salifert?

TIA

 

[leebca]

Habib,

Red Sea.

 

[Habib]

Habib,

Red Sea.

When I mix Red Sea to a salinity of 35 I find 360 mg/L.

Red Sea , IIRC, also claims it to have that value.

I'll check that salt also with another lab grade kit.

 

[leebca]

RichardS & MiddletonMark

I disagree. I care if my Ca is 375 or 475 when managing pH lowering effects on my system. I'd boost the 375 and maintain high alk to make sure that at the lower pH my specimens have easy access to as much Ca as they need.