Salifert v. Seachem Ca Test Results

[MiddletonMark]

Exactly Shoestring.

Habib's excellent response/attention doesn't mean that someone else does a terrible job.
It just means that Habib does a great job

I'm pretty happy with my experience with both.

 

[Shoestring Reefer]

Perhapse I can arrange a test in our club in October (our next meeting). We can compare test measurements against a standard(s) as well as ASW.

Habib, Randy, others: the question of a "standard" keeps coming up. Seriously, can anyone recommend an acceptable standard we can just buy? There must be something available commercially. Perhapse X parts of a know calcium solution + Y parts of a magnesium solution + Z parts water?

 

[Shoestring Reefer]

Exactly Shoestring.

Habib's excellent response/attention doesn't mean that someone else does a terrible job.
It just means that Habib does a great job

I'm pretty happy with my experience with both.

And I'm glad we have (at least) two test kit manufacturers that give us great support.

:thumbsup: to both!

 

[leebca]

The challenge of a standard is just that. . .a challenge.

What we need is a seawater standard. Anything else would be open for technical questions.

Maybe we need a salt mix, sans calcium additives and sources? That would require a salt mix that doesn't carry trace calcium quantities.

If we don't do it this way, it comes back around to whether or not the SeaChem reference is a salt-water reference or one developed for the test kit.

 

[JakStat]

Habib, Randy, others: the question of a "standard" keeps coming up. Seriously, can anyone recommend an acceptable standard we can just buy? There must be something available commercially. Perhapse X parts of a know calcium solution + Y parts of a magnesium solution + Z parts water?

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.

 

[BeanAnimal]

At this point, 'support' is not an issue. Before we worry about customer support, we need to determine why these kits differ and by how much. I think leebca is on the right track. It would be helpful for him to also duplicate Habib's tests. Habib has been involved in this and will benefit no matter how the results turn out. SeaChem may also be interested, but I have a feeling most of the other manufactureres could care less. Some of them strive to be accurate, others just "close enough".

Bean

 

[jfinch]

Lee, have you tried using the 5 ml syringe that comes with the Salifert kit to draw the 1 ml water sample for your Seachem kit? Maybe the sample pipette that came with your Seachem kit is off

FWIW, I find it very strange that these kits are that far off from each other. Testing for calcium is not rocket science. I bet most if not all test kits use the same basic indicator (maybe tweaked slightly by salifert/seachem/etc to sharpen the endpoint). There's a couple procedural steps that can lead to volume errors: sampling the tank water and titrating the EDTA. Both kits in question use 1 ml = 500 mg/l Ca on the titrant side giving similar potential volumetric errors (assuming they both use similar titrating syringes). On the water sampling side, the Seachem sample is only 1 ml while the Salifert sample is 3 ml. The larger sample size of the Salifert should reduce the magnitude of this error, shouldn't it?

Just another anecdotal data point... I get essentially the same values (within 10 ppm) when testing the calcium in my tank using the Salifert kit and a lab grade Hach test here at work.

 

[leebca]

I've actually used the 2 ml syringe that comes with the Salifert Magnesium kit to measure the 1 ml sample for the SeaChem Calcium Test. I too was skeptical of that plastic pipette, not to mention the lack of control in trying to get the water at the mark. I didn't see any difference in test results.

I agree that the larger sample volume would reduce the error. The SeaChem starts with 1 ml and adds distilled water to it. The Salifert starts with a 2ml sample. I would favor the Salifert kit giving a more reliable/sensitive result, having the larger sample size.

The syringes look the same to me, but the Salifert provides a fine tip attachment. This allows for smaller drops. But the SeaChem test kit offers the operator a choice to leave the tip under the surface of the test sample and stop dispensing at the color change (i.e., drops not important). I think for both, the drop size can be circumvented by touching partial drop off to the side of the sample tube or even submersing the tip in the sample. But, obviously, there must not be any mistake like drawing or allowing liquid to come back into the syringe if the operator uses the tip-in-sample method.

I've tried all the above variations. I find a cleaner/finer endpoint by touching the partial drop off just before the endpoint, taking a reading when I think the endpoint was reached, then adding a full drop more to verify I was at the end point.

I don't have a Hach kit. Couldn't find one easily so I gave up.

I can't/couldn't explain the difference. If it's something I'm doing wrong, at least I'm consistently doing it wrong!

Can you provide details on the two kits you're using? (Expiration date(s); reagent lots; etc.).

Thanks for your post. :rollface:

 

[Shoestring Reefer]

leebca-you can start with 2 ml in teh seachen test, just use twice the water then divide the amount of reagent 3 by 2.

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.

He he, your job description is "Scientist - Molecular Immunology". Sometimes I watch the Sci-Fi channel, or my wife watches CSI, and that's about as close as I get to a lab. But I CAN get a bunch of people together with some test kits. Before I bother, I might as well make shure it's worth our time.

So, how 'bout me buying a bottle of what we can agree to be an acceptable standard on the internet? Or somebody with a lab and some spare time can mail a standard to me. I can pm you my address, just don't get me on any more junk mail lists.

 

[leebca]

That's interesting about increasing the SeaChem sample. I'd end up having to fill the pipet twice.

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?

One of the drawbacks of some kits is that they work well with freshwater, but not so well with seawater.

 

[Boomer]

Lee

But Shoestring. . .One of the concerns about the test kits is their ability to measure calcium in saltwater

That has always been my argument for any test done in seawater. People often get themselves in trouble doing this. One may want to look at these test kits and see what interferences they have. You may be surprised. i.e, Mg higher than 200 mg / l , Sr and Ba are measured as Ca. I do not see any of them explaining it or if such corrections are made in their test kits. I know Habib is well aware of them.

It is not just Ca test kits in question, it is any test kit in question when used in seawater. All kits should be tested against a known seawater std, no matter what ion is in question.

Some kits say can be used in seawater but when you actually talk to the chemist, "well they can be but you would have to make up our own seawater stds." Know anyone that makes a seawater std for say NO3 in seawater :lol: This is an issue when using spectrophotometers for seawater. If you are testing for PO4 then these are just ducky

 

[Boomer]

Mike you hae been watching to much Battlestar Galactica

 

[leebca]

I use the LaMotte colorimeter for ammonia, iron, nitrate, and phosphate. They have a calcium test, but they insist it won't work with seawater. They also insist it won't work if I dilute the seawater.

I tried it anyway. They were right. The scatter was too great to be of value for me.

I'd think, being LaMotte, that if a Ca colorimeter test on seawater was possible, they would have provided something. Maybe not. But if the interference mentioned by you (Boomer) are significant, I can appreciate the challenge. :rollface:

A variance in test kits results could then be explained by how the kit addresses the interference (if it does at all), with each kit (or group of kits) handling intereference in a different way.

Thanks for your post, Boomer.

 

[Boomer]

Lee

nitrate

This will not work either, I talked to their chemist and is where I got

"well they can be but you would have to make up our own seawater stds." "

And the same answer from HACH. I posted it here when JFinch had questions on the HACH spectro

Mg higher than 200 mg / l , Sr and Ba are measured as Ca

This is from a HACH $120 Digital Titrator kit, which is suppose to be the most accurate kit there is for Ca. IICR you can adjust for Mg higher than 200mg /l by adding ??????????

I forgot iron and ammonia test fine on the spectro's

 

[leebca]

Do you like the Hach titrator? I was tempted, but didn't take the plunge. The compensating factor isn't known, or determined then used to adjust the Hach results? Your "??????" were unclear. What IICR are you using? or did the ????? pertain to the IICR.

My nitrate have come out supporting two other nitrate test kit results, plus nitrates tested by AA. This is what gave me the confidence to use it. I do make a 1:10 dilution and the results are within 10% of the AA. I'm using their low level Nitrate reagent set (#3649-SC) and an occasional double check with a test kit and AA. But you're right, it wasn't made for that, and they said the same to me.

 

[leebca]

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

 

[BeanAnimal]

What this means to me (correct me if I am wrong...)

1)* Habib has tailored his kit to give "correct" results when testing a "KNOWN" seawater sample.

2) Other maufacturers have tailored their kits to give a "correct" result when testing a "standard"


This may explain why the Ca readings from Salifert differ from the other kits. Or in other words, the Salifert kit is correct, the others are wrong due to interference (or lack of). After all we are testing salt water, not standards.

*Now the "KNOWN" seawater sample is another question that I have seen up for debate here. Habib me be testing against NSW, but how does he know what it's true Ca concentration is.

This is starting to sound like trying to get a photo ID without a photo ID. If you have lost all of your indentification there is nowhere to start.... We seem to have kits that measure "stuff". We have no known quantity of "stuff" to measure against.

If I am wrong, please let me know.

 

[BeanAnimal]

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

 

[jfinch]

Can you provide details on the two kits you're using? (Expiration date(s); reagent lots; etc.).

I'll get the info on the Salifert kit when I get home.

The Hach method uses Hach calcium indicator CalVer 2 powder pillows (Hach Cat # 852-99). A 5 ml sample using a lab grade pipette is sampled. The pH of this sample is adjusted to at least 13 using 0.1 N KOH. The powder pillow is added and the sample is titrated from pink to blue using 0.01 N EDTA using a lab grade burret. This is essentially the same method as the hobbyist kits just using better equipment.

You may be surprised. i.e, Mg higher than 200 mg / l

Yes, seawater samples don't have as distinct endpoint as freshwater using the Hach indicator (the transition from purple to blue is VERY long), but since the results I got from this method and my Salifert kit matched, I didn't worry too much about it. Maybe they're both wrong

I posted it here when JFinch had questions on the HACH spectro

Yeah... that was and still is a bit of a bummer. But I can still use that machine for phosphate

 

[Boomer]

Hach titrator?

I loved it I had the whole run of them 100's of dollars worth. I can not give you an answer, it has been years. I gave them all to Randy and he has not played with them yet. More than likely will have to get all new reagents. I do not remember what the ??? which is added to the sample IIRC to compensate for higher than 200 mg.


Aaah wait I still have the manual.........................

Ok, pg 79

Interference from Mg up to 200 mg / l is prevented by the formation of magnesium hydroxide at the high test pH but prevents a distinct end point above this level.

Calcium is titrated with EDTA, after removing Mg interference by pH adjustment. After all Ca in the sample is complexed by EDTA, CalVer2 indicator changes color from red to blue, signaling end-point.

It also says as I stated earlier that Sr and Ba are measured as Ca. Potassium cyanide is also added to stop any inter with cobalt, cooper, nickle and zinc. Iron inter if over 8 mg / l and Mn if over 5 mg / l. Al at over 200mg / l and Acd and Alk over 10,000 mg / l. Also solutions saturated with NaCl. PO4 can cause a slow end-point. Polyphos must be absent.