Lamotte, Red Sea, Salifert ALK Tests Evaluated

[JimWelsh]

What do you mean they also test for carbonate?

I believe ATI reports a "Carbonate hardness" value in dKH units, e.g. ATI ICP Test - Results Are In!

I wonder if that means that they titrate for total alkalinity, and then use the ICP boron value to calculate borate's contribution to total alkalinity, and subtract that out to arrive at "Carbonate hardness". If so, that might explain why their "dKH" values are lower than a careful hobbyist's total alkalinity "dKH" values.

 

[Randy Holmes-Farley Verified Community Expert]

Might be worth asking them, although I suspect it is total alk they are reporting and just call it carbonate hardness.

 

[David S]

What do you mean they also test for carbonate?

Why would there be a relationship between ATI results and Salifert?

Yes, indeed.
ATI tests for Carbonate.
They also provide ICP testing for your seawater as well as your RODI water. All in one package.
ATI's carbonate result was 6.84 DKH and as best I can recall, my corresponding Salifert result was near 8 DKH.
In all honesty, though, I may not have used the Lavender colored endpoint. Still, I'm sure it would have been significantly higher than the ATI result

 

[Oldreefer44]

I tested with Red Sea, Salifert and Hanna. Hanna's results were 5.8 DKH. Both Red Sea and Salifert were 8.1. Sent to ATI which came up with a result of 5.8. Have a hard time trusting anything at this point when there is that much deviation.

 

[David S]

I tested with Red Sea, Salifert and Hanna. Hanna's results were 5.8 DKH. Both Red Sea and Salifert were 8.1. Sent to ATI which came up with a result of 5.8. Have a hard time trusting anything at this point when there is that much deviation.

That's interesting-and somewhat unexpected.
Were you using the current Red Sea Kit (green endpoint) or the old one (orange endpoint).

FWIW, the pH 4.5 Buffer Powder Pillows referenced in this post are made specifically to check the endpoint color of an alkalinity titration: DIY Alk test discussion thread

Jim
Let me know if I got this straight:
If I add one of these Hach "pillows" to the specified volume of water and then add any of the reagents I will eventually see ONE color which is the actual endpoint for each particular reagent?

 

[Randy Holmes-Farley Verified Community Expert]

Yes, indeed.
ATI tests for Carbonate.
They also provide ICP testing for your seawater as well as your RODI water. All in one package.
ATI's carbonate result was 6.84 DKH and as best I can recall, my corresponding Salifert result was near 8 DKH.
In all honesty, though, I may not have used the Lavender colored endpoint. Still, I'm sure it would have been significantly higher than the ATI result

I think that is likely not true unless they specifically told you they test for carbonate.. You can not detect carbonate by icp. It can be arrived at as Jim noted by measuring total alk and subtracting some other things. I doubt they do this, since it is potentially erroneous and complicated.

 

[Randy Holmes-Farley Verified Community Expert]

That's interesting-and somewhat unexpected.
Were you using the current Red Sea Kit (green endpoint) or the old one (orange endpoint).

Jim
Let me know if I got this straight:
If I add one of these Hach "pillows" to the specified volume of water and then add any of the reagents I will eventually see ONE color which is the actual endpoint for each particular reagent?

You add just the indicator dye, not any of the acid titrant. It shows the color that that specific indicator dye shows at pH 4.5.

Same could be done with a pH meter instead of the powder pillow, since all it does is provide a pH 4.5 solution.

 

[David S]

You add just the indicator dye, not any of the acid titrant. It shows the color that that specific indicator dye shows at pH 4.5.

Same could be done with a pH meter instead of the powder pillow, since all it does is provide a pH 4.5 solution.

Thanks Randy

 

[Lunger50]

FWIW
Did a test earlier this morning using the Red Sea and Salifert kits.
I used the Lavender coloration (the drop just prior to the sample showing a hint of pink color). The DKH still exceeded the Red Sea result by 0.3+ DKH.
My gut feeling is that while the Salifert kit gives very consistent results, the numbers run high.
I am not just basing it on the fact that the Lamotte and Red Sea tests give lower (and similar) results compared to the Salifert but more so based on the Alkalinity results that I got when I did an ICP test with ATI, one year ago.
They also test for Carbonate in DKH and I noticed that their result was almost 1 DKH lower than my result.
At the time, I was only using the Salifert test.
I hadn't started using the Lamotte test yet and while I had a Red Sea kit, it was the older version (orange end point) which I had no confidence in and didn't bother to use.
I was so confident in the Salifert result that I questioned ATI about their result.
As they did not have any remnants of my original sample, they offered to run the ALK test twice when I submit my next sample.
Have not done any ICP tests recently, but the next time I do I'll consider ATI so I can compare my 3 test kits with their results.
So my question is; has anyone tested with ATI, who also use a Salifert kit, and if so were there similar discrepancies?

Do you know the actual ALK of the water your testing?

Essentially you are simply testing kits against each other, that's cool, but without knowing the actual ALK of the water your testing which ones are closest to accurate? You have stated that Salifert tests high, is it not plausible that the other two kits test low and the Salifert kit is indeed accurate?

 

[David S]

Do you know the actual ALK of the water your testing?

Essentially you are simply testing kits against each other, that's cool, but without knowing the actual ALK of the water your testing which ones are closest to accurate? You have stated that Salifert tests high, is it not plausible that the other two kits test low and the Salifert kit is indeed accurate?

That's a possibility, but as I previously stated the Salifert result was similarly elevated compared to a 3rd party (ATI) evaluation, as well.

 

[Randy Holmes-Farley Verified Community Expert]

That's a possibility, but as I previously stated the Salifert result was similarly elevated compared to a 3rd party (ATI) evaluation, as well.

Maybe they use the Red Sea kit.

 

[David S]

Maybe they use the Red Sea kit. [/QUOTE

LOL
But that was the old kit, which was actually prone to higher readings.

 

[JimWelsh]

Do you know the actual ALK of the water your testing?

Essentially you are simply testing kits against each other, that's cool, but without knowing the actual ALK of the water your testing which ones are closest to accurate? You have stated that Salifert tests high, is it not plausible that the other two kits test low and the Salifert kit is indeed accurate?

Good point. Also, FWIW, I'd like to add in my experimental experience with regards to this issue. Please see my prior comments about this here: DIY Alk test discussion thread and here: [URL="https://www.reef2reef.com/threads/salifert-kh-alk-testing-help.311941/#post-3841028"]Salifert KH/Alk testing help.

TL;DR = I have carefully created alkalinity standards in an ASW matrix, and found the correct equivalence point of the Salifert dye to be this "lavender" color.


[/URL]

 

[David S]

I guess the clincher would be to use Randy's DIY "acid" test and compare those results with each of the test kits.
Trouble is I currently don't have a PH monitor/probe as I rarely find the need to test PH (API).
It is tempting, though, and if I got a real good deal on a PH monitor, I might pull the trigger.

 

[JimWelsh]

https://hannainst.com/hi12302-halo-...MInuqY5cPN3wIVBh6tBh0bbQcoEAQYBSABEgLuNPD_BwE

 

[David S]

Nice, Jim
But a bit out of my price range.
Was considering a Pinpoint, which seems to be the moderately priced one of choice.
Hopefully catch one on sale.

 

[David S]

Just by chance Premium Aquatics has an after New Year's Sale so I sprung for a Pinpoint PH Monitor with probe.
Then went to Ebay to purchase 1 liter of 0.1N solution of HCL.
When I receive them, I will conduct tests for the aforementioned kits, as well as, perform the DIY test.
Hopefully, this will bring some clarity as to the accuracy of the test kits.

 

[David S]

Sorry Randy
I inadvertently deleted a character which caused my reply (below) to appear as it came from you:

LOL
But that was the old kit, which was prone to higher reading interpretations

 

[Big E]

Final Results
In all 3 testings the results from the Lamotte and Red Sea test kits were virtually identical.
In each case the Salifert result was 0.5 - 0.6 DKH higher.

I've used a LaMotte kit many times over the years to back test my Salifert kit and my results were always the same as what you tested. Salifert approx .5 higher.

It really didn't matter which was right but more so I know that the Salifert I use all the time was consistent and reading correctly.

 

[David S]

OK
Finally got the Pinpoint PH Monitor Probe. Already on hand were the 0.1N HCL and PH 7.0 & 4.0 buffer reagents.
To measure my test water, I used a digital scale I bought on Ebay some time ago. It's proven reliable, in the past, and I have no reason to believe it is any less so now.
I measured out approximately 256 - 257 grams to get my 250 ml of test water .
I planned to place it in a glass measuring cup (not really to measure but simply to hold the sample). However, my wife would not hear of it, so I ended up placing it in a plastic measuring cup, instead.
I used two hobbyist syringes; one 5 ml and the other 2 ml to administer the HCL, since I did not anticipate the amount of acid I needed to exceed 7 ml, as I keep the Alkalinity in my tank between 6.7 - 7.3 DKH.
As it happened, the amount of acid needed to get ~4.50 PH was more than expected. I stopped performing the procedure when after shaking the sample the PH was 4.49. After a minute or so it settled to 4.52. The amount of acid used was ~6.74 ml.
Using Randy's formula, that equates to ~7.55 DKH.
This was more than I keep my Alk at; at least based on the Red Sea & Lamotte results, I've been getting for months, although it was quite in range of the Salifert kit.
I also abstained from adding some Alkalinity, yesterday (Monday), which is usually my custom. The intention was to insure a lower (<7.0) DKH.
Because of the higher than expected readings, I performed a 2nd test. In this instance, the PH endpoint was 4.45 and the amount of acid needed was ~6.60 ml. This equates to a 7.39 DKH.
Splitting the difference between the 2 samples yielded a DKH of 7.47

As for my test kit results:

The Red Sea tested at ~6.7 DKH. I used a pale green result, just before it reached the beyond endpoint coloration (yellow).
The Lamotte result calculated @ 6.72 DKH. The result I used showed the end color with just a slight hint of the beyond endpoint color.
As for the Salifert kit, it tested at 7.3 DKH. This was based on the lavender coloration. However, by adding 1 more drop, I got a slight pink coloration, similar to the photo supplied with the kit. That single drop brought the DKH up to ~ 7.5.

The results are an eye opener for me - to say the least.
I fully expected the "acid" test to corroborate the accuracy of the Red Sea & Lamotte test kits, instead it appears quite the opposite.
I was swayed by the majority rules, based on the similarity of the Red Sea and Lamotte results.
In addition, the fact that the Lamotte kit is more expensive, no doubt, added to an overall bias on my part.
This in spite of the fact that I have used Salifert kits for years, and been very satisfied with their accuracy.

Randy, Jim

I want to thank you for suggesting the use of the Acid testing. Will definitely make use of it in the future.