Salifert v. Seachem Ca Test Results

[Boomer]

Bean read this it may help you Even a $80,000 toy is not sure :lol:


http://www.reefkeeping.com/issues/2005-04/rhf/index.php


For initial testing I chose to use as the "standard" a sample of artificial seawater that was mixed to an approximate salinity of S=35. I mixed a 44-gallon batch using Instant Ocean artificial salt mix and reverse osmosis/deionized (RO/DI) water to a conductivity of 52.7 mS/cm, and allowed it to settle for three weeks. I then proceeded to measure its calcium concentration by ICP-AES (inductively coupled plasma-atomic emission spectroscopy, an $80,000 analytical instrument. I was somewhat disappointed with my inability to use this sophisticated technique to get a precise answer. Despite taking five different samples and analyzing them at eight different emission wavelengths using two different calibration methods (five standard additions of known calcium concentrations to each sample, as well as comparison to a fixed 1000 ppm commercial calcium standard), I was unable to get consistent values. Some of the samples were acidified or filtered through submicron filter membranes to determine if solid materials were impacting the result (they were not). Overall, I took more than 200 measurements, each involving three replicate observations of the emission intensity. Nevertheless, the result was not very satisfying, with a substantial variation occurring between the different values. The average of every measurement taken was 336 ppm. With the uncertainty involved, however, I'd conclude that the true value was probably 340 Ã"šÃ‚± 40 ppm. I also measured the same sample once with a Salifert brand test kit and got 330 ppm calcium.

Looks like the Salifert did very well against a $80,000 toy

 

[JakStat]

Well at least Seachem got the correct control; the standard should be seawater as Boomer stated.

I'm currently using Seachem myself, but have used Salifert previously. Regardless of the current line of discussion, in general I really really like having a reference or positive control when I'm doing any assay. If Salifert included this I think it would be a great selling point and very appropriate.

How does SeaChem or Georgia know that the calcium content os correct if it is so hard to measure?

Because the reagents are measured out during prep. If you make a reagent of known molar concentration, then it's known. The value can then be easily converted to ppm, mg/mL.

BTW Boomer thanks for posting the Ca test reagents and "protocol", I've been vaguely wondering about that for a while now.

 

[Habib]

Lee,

Thank you for correcting your comments regarding the calcium content in the REd Sea salt.

You asked about the source water. I use DI water with a very high resistivity (low conductivity). That water contains far less than 1 ppm of calcium.

I typically find 360 ppm when made at full strength (35 PSU).

My Red Sea Insert says:


Thus, in my case, I'd expect about a 355 ppm Calcium on the Red Sea makeup water, which was what the Salifert Test Kit said it was, but 250 was the SeaChem result. Then I used the SeaChem reference to do more testing. The span was there on that reference sample. It was apparent to me (and still is) that a wider sample selection needed to be tested, with a wider selection of test kits, and the AAS.

Habib, when you earlier wrote: [/b] what were you using as the source water? Why were you assuming what my Calcium results should be, not knowing my makeup water content?

I'm still hoping to resolve the concerns through a wider matrix of testing, and the AAS. [/B]

 

[Habib]

Lee,

quote:
--------------------------------------------------------------------------------
Habib said:

. . .we use various natural seawaters for which the calcium concentration is known. .
--------------------------------------------------------------------------------

Known how? Using the Salifert kit? If you're going by general assays and not actual measurements, I can see a source for error.


What I addressed is the large discrepancy of approx 25%.

I showed how the Salifert responded to a commercially cerified standard. I also showed how it responds to NSW.

NSW if collected away from the shore and if there is no input from rivers then the calcium concentration is known if the salinity is known (check it, or ask some seawater chemists).

We have many many many more methods of checking this but the discussion is a difference of 25 % not only a few percents.


I'm 100.0% sure that our kits give the right result.

BTW, FWIW, I saw on another board someone else also mention a 100 ppm difference between the Seachem and Salifert.

I also saw on this board someone mention the same difference beteen teh AP Ca test and the Seachem.

 

[Habib]

I finally contacted SeaChem Technical Support.

I was told their reference solution:

1) Is seawater;
2) Is analyzed by Georgia University for Calcium content.

I didn't get any other info, but they can be called for more info: 888-732-0003

You must have missed the threads/ posts about it.

My post after:
http://www.reefcentral.com/forums/showthread.php?s=&postid=5516462#post5516462

 

[Habib]

Anyone with lab access (molecular bio, chem) could make this in 5 min. It should just be a calculated concentration of Ca, perhaps as CaCl2. If you do the molar calculations, conversions and prep right, the concentration can be known to an extremely accurate degree.

Besides being not (fully) suitable for all type of calcium kits one also neeeds to know the exact amountof water in the CaCl2 since it picks up moisture rapidly.

So a real standard can't be made this way.

FWIW, I have suggested this but only to show if the kit is really giving a 25% higher result but that is soemthing different than a really good standard.

 

[Habib]

To set a few things "straight"

I pm-ed Leebca a few days after this thread died, that was after the first 4 or so posts.

I sent the pm because there was something wrong in Lee's posts. He found higher values on the saltmix but lower on the Seachem ref using the Salifert kit.

I was worried he might be doing something wrong.

So I don't think, so far, that Lee has interests in a any particular company.

However, things like that happen occasionally so it is always good to be alert.

BeanAnimal gets points for intelligence.

No points for RustySnail.

I work for a company that manufactures high pressure aluminum gas cylinders. I am a marine aquarium hobbyist of 36+ years. One degree in Chemistry; one degree in Microbiology, from OSU.

It's interesting to note that my posts are being taken as 'bashing' at least by one willing to write about it. I think I was and am still keeping an open-mind here. I want to know the facts and right now, there is too little information to come to any informed decision. As I stated much earlier, both Salifert and SeaChem are reputable organizations. Errors and weak assumptions do occur. But as the top post of this thread states, I can't make a credible Calcium addition when test results show a large range of possible Calcium concentrations.

Regarding Habib's involvement and contributions: Many people have done that in our hobby. Yet what they have to say and believe doesn't mean it is fact or truthful. I am appreciative of his involvement --- of EVERYONE'S involvement here at RC.

It's amazing to me, having read thousands of posts here and on other forums, how one minute the posts run from "don't trust him/her/them, because all they want to do is sell" to "he's a good guy, believe him." The fact is, I separate the information from the source and give no more credibility to the owner of a company or name on a product (e.g., Julian Sprung, Mark Weiss, etc.) than to the novice who just reported an event. Our hobby is full of anecdotal information. I mostly trust the published scientific studies, but even they are tainted by the occasional competition for grant monies.

It's rare we can investigate for ourselves in this (overly expensive) hobby. (I'm unsure what I will do with all these left over kits!) I will do investigative work when I can and I will share the information. As an undergraduate at OSU I studied Cryptocaryon irritans, use of antibiotics to fight it (including garlic), dips and baths, immunity, and fish nutrition. I was funded for these projects. It's much harder on your own!

It may surprise the readers of this post that all I will be providing is data and results, no conclusions. This is not a scientific project or study. Draw your own conclusions. But, RustySnail, just do your own study and stop reading my posts if you are convinced my motives are of such low integrity.

 

[JakStat]

Besides being not (fully) suitable for all type of calcium kits

Ok then, as I suspected, the standards may not be cross-compatible across brands.

And then, the test comparison we're talking about here using the same standard for both brands might be mucked up by that.

Habib did you say the standard you use is in freshwater? Since Seachem's is in seawater perhaps your test is optimized differently.

:strooper:

one also neeeds to know the exact amountof water in the CaCl2 since it picks up moisture rapidly.

So a real standard can't be made this way.
[/B]

so open a fresh bottle... hygroscopic reagents aren't black boxes. Besides, that consideration is for anhydrous, you can get hydrated CaCl2 from Fisher or VWR (I believe it's dihydrate). If one has the molecular reagent-grade like most MoBio labs do (for purifying DNA vectors) then you can cross that off the "to-worry-about" list. Reagents like that have to be exact, we don't go around checking concentrations on mass spec on all the solutions we cook up, and they almost always have to be dead-on.

 

[Boomer]

NSW if collected away from the shore and if there is no input from rivers then the calcium concentration is known if the salinity is known (check it, or ask some seawater chemists).

The Law of Equal Proportions If the salinity is 35 ppt vs 31 ppt there will be a lower Ca level by the % of drop in salinity. That is a 12 % drop, so if the Ca was 410 mg / l then it will equal a 12 % drop in Ca = 360 ppm Ca. And if you look at ion ratios, such as Mg:Ca, the ratios will still be the same 3:1, Mg at 1135 mg / l, Ca 360 mg / l, if we assume std was 410 Ca and 1290 Mg @ 35 ppt @ 25 C @ 1 ATM.

 

[Habib]

Our kit is suitable for both freshwater and seawater.
However it is slightly less accurate for freshwater.
We make sure that the highest accuracy and precision is obtained when using seawater with or without major fluctuations in the matrix and also salinity.

The test is designed for reef/marine aquaria and performs quite well on freshwater.
However, freshwater does not contain that high calcium as seawater and a standard made with frshwater and containing a high calcium concentration can be problematic but there is a work around.

The Seachem's "reference" is not seawater but their saltmix according to the owner of Seachem (see the link I gave in a previous post).



Even the hydrated CaCl2 such as the dihydrate or hexahydrate are highly hygroscopic.

Ok then, as I suspected, the standards may not be cross-compatible across brands.

And then, the test comparison we're talking about here using the same standard for both brands might be mucked up by that.

Habib did you say the standard you use is in freshwater? Since Seachem's is in seawater perhaps your test is optimized differently.

:strooper:



so open a fresh bottle... hygroscopic reagents aren't black boxes. Besides, that consideration is for anhydrous, you can get hydrated CaCl2 from Fisher or VWR (I believe it's dihydrate). If one has the molecular reagent-grade like most MoBio labs do (for purifying DNA vectors) then you can cross that off the "to-worry-about" list. Reagents like that have to be exact, we don't go around checking concentrations on mass spec on all the solutions we cook up, and they almost always have to be dead-on.

 

[Habib]

NSW if collected away from the shore and if there is no input from rivers then the calcium concentration is known if the salinity is known (check it, or ask some seawater chemists).

The Law of Equal Proportions If the salinity is 35 ppt vs 31 ppt there will be a lower Ca level by the % of drop in salinity. That is a 12 % drop, so if the Ca was 410 mg / l then it will equal a 12 % drop in Ca = 360 ppm Ca. And if you look at ion ratios, such as Mg:Ca, the ratios will still be the same 3:1, Mg at 1135 mg / l, Ca 360 mg / l, if we assume std was 410 Ca and 1290 Mg @ 35 ppt @ 25 C @ 1 ATM.

Yes.

Thanks!

 

[leebca]

So is the ppt of the water is assumed or is it measured and the Ca calculated?

I can't speak for the machine you've referenced Habib, but current lab analysis uses a Atomic Absorption Spectrophotometry equipment like a Perkin Elmer AAnalyst 200. The sample is diluted 1/100 and is essentially a freshwater sample. The standard is dried, purified Calcium carbonate. Some hype on the equipment is on the Perkin-Elmer site: http://las.perkinelmer.com/Catalog/ProductInfoPage.htm?ProductID=B3150070

I will include that machine's results in my test matrix.

 

[boxfishpooalot]

so in short,so I dont have to read all of it, what have you guys discovered between the two?

 

[Habib]

Lee,

The salinity is measured and is within 1% of the salinity cited in the literature for the areas in which they were collected.
We have many NSW from various locations.
Besides the salinity check also the calcium value is verified in various ways. So we are pretty sure of the calcium values in the NSW samples.


I can't comment yet on AAS but with all such instrumental techniques the base line and noise and errors in dilution can be problematic.

FYI, with some instrumental techniques we use it takes almost a day to make an accurate measurement. Most of the time takes the making of fresh calibration lines, checking them, making the dilutions by weight and doing several standard additions (also by weight).


The calciumcarbonate will be problematic.
Too little acid and not all will be dissolved giving erratic readings and the test kits too.

Too much acid and the test kits will not be able to adjust the pH to the desired values, which can vary from barnd to brand.

So is the ppt of the water is assumed or is it measured and the Ca calculated?

I can't speak for the machine you've referenced Habib, but current lab analysis uses a Atomic Absorption Spectrophotometry equipment like a Perkin Elmer AAnalyst 200. The sample is diluted 1/100 and is essentially a freshwater sample. The standard is dried, purified Calcium carbonate. Some hype on the equipment is on the Perkin-Elmer site: http://las.perkinelmer.com/Catalog/ProductInfoPage.htm?ProductID=B3150070

I will include that machine's results in my test matrix.

 

[boxfishpooalot]

habib, could you find that article I posted in your forum? The one with the ammonia test kit, where you took pictures of each measurment for me. I cant find it.

I think it was called ammonia test kit.

That was the article I got superor customer service/help. Imo.


Edit, actually I think it got deleted because its old.

 

[Habib]

habib, could you find that article I posted in your forum? The one with the ammonia test kit, where you took pictures of each measurment for me. I cant find it.

I think it was called ammonia test kit.

That was the article I got superor customer service/help. Imo.


Edit, actually I think it got deleted because its old.

Threads don't get deleted unless there is a very good reason for it.
You can set the date upto which the threads are shown to the beginning at the bottom of each forum.

I'll pm you the link.

 

[Habib]

Lee,

FYI, besides what I alreday said and Boomer posted:


Constant Proportions

Seawater is a well-mixed solution; currents and eddies in both surface and deep water, vertical mixing processes, and wave and tidal action have all helped to stir the oceans through geologic time. Because of this thorough mixing, the ionic composition of open-ocean seawater is the same from place to place and from depth to depth. That is, the ratio of one major ion or seawater constituent to another remains the same. Whether the salinity is 40ââ"šÂ¬Ã‚° or 28ââ"šÂ¬Ã‚°, the major ions exist in the same proportions. This concept was first suggested by the chemist Alexander Marcet in 1819. In 1865 another chemist, Georg Forchhammer, analyzed several hundred seawater samples and found that these constant proportions did hold true. During the world cruise of the Challenger Expedition (1872-76), seventy-seven water samples were collected from different depths and locations in the world's oceans. When chemist William Dittmar analyzed these samples, he verified Forchhammer's findings and Marcet's suggestion. These analyses led to the principle of constant proportion (or constant composition) of seawater, which states that regardless of variations in salinity, the ratios between the amounts of major ions in open-ocean water are constant. Note that the principle applies to major conservative ions in the open ocean; it does not apply along the shores, where rivers may bring in large quantities of dissolved substances or may reduce the salinity to very low values. The ratios of abundance of minor non-conservative constituents vary, because some of these ions are closely related to the life cycles of living organisms. Populations of organisms remove ions during periods of growth and reproduction, temporarily reducing the amounts of these ions in solution. Later, the population declines, and decay processes return these ions to the seawater.



This still holds untill today.

 

[Shoestring Reefer]

But Shoestring. . .One of the concerns about the test kits is their ability to measure calcium in saltwater. If you use a freshwater standard, will that be representative of the kit accurately measuring calicum in saltwater?

I'm not looking for a "freshwater" standard. I'm just looking for an "acceptable" standard.

NSW if collected away from the shore and if there is no input from rivers then the calcium concentration is known if the salinity is known (check it, or ask some seawater chemists).

The Law of Equal Proportions If the salinity is 35 ppt vs 31 ppt there will be a lower Ca level by the % of drop in salinity. That is a 12 % drop, so if the Ca was 410 mg / l then it will equal a 12 % drop in Ca = 360 ppm Ca. And if you look at ion ratios, such as Mg:Ca, the ratios will still be the same 3:1, Mg at 1135 mg / l, Ca 360 mg / l, if we assume std was 410 Ca and 1290 Mg @ 35 ppt @ 25 C @ 1 ATM.

OK, I actually remember that from chemistry (and a few reefing books): the ratio of major ions are conserved. Maybe there's a more scientifically accurate way to say it, but I get the jist.

Is everyone in agrement that if a sample of NWS (taken from a reasonably "clean" area, not next door to a calcium plant in a third-world country) can have its salinity accurately measured, the calcium concentration in that sample can be determined and it will be a good reference for checking calcium tests?

If so, I propose to test several calcium tests with the following "standards"
-Natural Sea Water of accurately known salinity, thus known calcium content
-SeaChem calcium standard (I have a fairly new test with an unopened bottle)
-Artificial Sea Water of accurately known salinity (but not necessarily known Ca content, based on how much you trust manufacturer's data and quality control), newly made (perhapse the night before), from at least one brand.

Differences in the test's accuracy when measuring known standards is interesting, but their ability to measure ASW is of more importance to most reefers since that's what's in our tanks. Consistantly different readings from different brands presents a communication obsticle; ie, "my Ca is at 375 and his is at 375, why can't I grow corraline if he can?" Answer = his Ca is really 450, or yours is really 300, and you're using different test brands. Who knows, someday we may end up with different recommended calcium measurements based on different test kit brands, which might actually be beneficial. Or, the test kits might all work pretty much the same.

I'll make it a "blind" test, nobody will know what the NSW CA reading should be.

 

[leebca]

I have confidence in a machine's ability to measure something when I can count on a high correlation coefficient (r value) the standard curve generates. If the machine can't produce no less than a .99 r value, it isn't a very useful tool. This can be determined even before unknown samples are evaluated by the machine.

If the correlation coefficient of the ICP-AES doesn't or can't provide a high r value, it's not a useful tool. I don't know its r value.

The AAS has a high correlation coefficient on standards and knowing its ability, I do have confidence in it.

The analytical chemist part of me won't accept "If we know the ppt of sea water than we know the Calcium content of it." The theory may be sound, but when it is proven by data and the test for ppt has been shown to be referenced to known standards, I may begin to believe. But a calculation based upon a test of another condition, to determine calcium concentration has the potential for too much error. We may just have to agree to disagree on this one. I can't accept what it 'should' be to form the foundation of reality.

If seawater is so well mixed, then why does the Gulf Stream exist? Too much can wrong with making assumptions necessary to say, 'We know the calcium content because water is well mixed and we know the ppt.'

 

[Habib]

I am really amazed with what ease you trust (or is it trusted) a reference supplied in a hobby test kit but don't trust what are facts presented in the scientific literature and fully accepted by the scientific community. It is something which is in standard textbooks of oceanography and marine chemistry.



I have confidence in a machine's ability to measure something when I can count on a high correlation coefficient (r value) the standard curve generates.

Producing high correlation coefficient and low s.d. does not mean that the result is accurate.