"old" reagents ... Specifically hanna alk solution

[BryanM]

I would interpret as 10.7

The Marine master alk test has accuracy +/- .3 dkh so if the water is truly 10.7 then you could test multiple times and get readings anywhere from 10.4-11 and it would be within spec for that test kit.

That's fair, the tests were over a 2 week period tho, and kept rising.

Service folks tested it at 9, and new reagent is testing in the same area.

 

[JonasRoman]

Old is in quotes because its not even a year old.

But basically its been testing 10.5, 10.7, 11, and I've been backing OFF my dosing to get this lower, and I just didn't believe it.

I had corals delivered by a local vendor and they nicely tested my alk - 9.0.

I get new reagent, 8.5.

I now have a salifert as a backup when numbers don't seem to make sense, but this testing error that I do not think is my fault is super frustrating.

(Hanna marine master tester, all vials rinsed with rodi and stored with rodi in them).

I think reason could be that after some time the acid in the reagent is contamined (by the pipette for instance) meaning the acid will be less strong. Then the kh results will be false high.

 

[mboley]

Somewhere I read that the Hanna Alk reagent only lasts a month. I found that answer after I started seeing much different readings versus a Salifert test. Frankly I dont remember if it was higher or lower. The owner of Kung Fu corals told me he experienced the same thing and just uses Salifert.

 

[Randy Holmes-Farley Verified Community Expert]

Somewhere I read that the Hanna Alk reagent only lasts a month. I found that answer after I started seeing much different readings versus a Salifert test. Frankly I dont remember if it was higher or lower. The owner of Kung Fu corals told me he experienced the same thing and just uses Salifert.

While I do not use the Hanna for alk, the one month seems excessively short.

 

[JonasRoman]

Somewhere I read that the Hanna Alk reagent only lasts a month. I found that answer after I started seeing much different readings versus a Salifert test. Frankly I dont remember if it was higher or lower. The owner of Kung Fu corals told me he experienced the same thing and just uses Salifert.

I would say thats not fully correct or a simplification.
As long as you don't open it it lasts probably for years.
This is same for all reagents. Expiry date on bottlealways means not opened bottles.
Once opened it can be contaminated, and some reagents more sensitive to that. As alkalinity reagents are acid its vulnerable to open and close bottle several times and especially contamination with not clean pipette.
If you are very careful with the pipette, never push back not used reagent back, and keep the pipette not touching other things when not used, the reagent will last long time. This is same for other kh reagents aswell where you manual interact with a pipette that can be contaminated.

Jonas

 

[billyocean]

Keeping the hanna alk reagent refrigerated and shaking before use keeps it steady in its readings for longer. Plus, there's the Hanna HI772 (dkh) and the Hanna HI755 (ppm) tester. I have the 772 and have received the 755 reagent and it was about .8 off. Makecsure the reagent number matches your hanna model #. Was told by hanna they were interchangeable but IME they weren't. That issue could be fixed by now..I dunno.

 

[JonasRoman]

Keeping the hanna alk reagent refrigerated and shaking before use keeps it steady in its readings for longer. Plus, there's the Hanna HI772 (dkh) and the Hanna HI755 (ppm) tester. I have the 772 and have received the 755 reagent and it was about .8 off. Makecsure the reagent number matches your hanna model #. Was told by hanna they were interchangeable but IME they weren't. That issue could be fixed by now..I dunno.

They are interchangeable. Its just a software converting factor where ppm×0.056=dKH
Refrigerated should be avoided! That can destroy the pH dye reagent . Its simply a ph dye combined with acid. The pH dye I think is bromocresoolgreen, maybe combined with one more to widen the ph range where we can see a difference in absorbance. If you refrigerate that it may loose its properties.

The reason of inaccuracy for Hanna alk is mostly based on the main method that is not a standard measure alkalinity. Normally you titrate and adding volume of acid is same as alkalinity. Thus volumetric titration. Hanna simplify this by add a constant amount of acid and then read final pH. As final ph is NOT linear to initial alkalinity when adding a constant amount of acid, the accuracy is its weakness. You have a quite narrow ph interval where we can see diff8in absorbance meaning the initial alkalinity must be within quite narrow intervals to give reasonable accuracy. When you are at the end, like kh below 6 or above 9, the accuracy is getting worse and above a certain alkalinity its impossible for this method to measure at all. Even with combined reagents its very narrow.
This is the same method simple stick tests for pool uses. Can never be accurate.

A standard titration kit is much much more reliable and accurate and has an endless measure range. And faster, and cheaper...

AMO Hanna checker for dKH should never be used of that reason. Its too many compromising with a fixed acid adding method.