Important findings according how to store open bottles of the reagent for Hanna Marine alkalinity checkers

[Doglips56]

There is a way to hinder the Hanna alk to show lesser and lesser dKH (or ppm for that matter) with age of open reagent bottle. I had the same story as many have reported here - my reading decrease from a new open bottle with time. Double check with another method show that there was not a real decrease - only that the reagent did not give the colour it should. Comparing with a fresh newly open bottle confirm the false readings of the old reagent. I did a test with shaking the bottle every time I use it - not better result. After this I start to store all open bottles in my refrigerator and voila - it works and give the right readings all the time. I have tested this for 8 months now and comparing with other types of measurements - the last bottle is now 4 months old (open) and still give the same result as my other tests (and a brand new opened bottle)

My findings - Store the open reagent bottle in a refrigerator, shake before use, It works with the cold reagent directly taken from the refrigerator

Other way to handle the test is to always use the same vial, use the same syringe and tip and clean the vale now and then with citric acid

Edit - the period I had tested it - checked my logs - it was 8 months not 6

Sincerely Lasse

Really appreciate you passing this info along. Now I’m questioning all my readings even though they’ve been fairly consistent. Will buy a new bottle and refrigerate. Thanks!

 

[Randy Holmes-Farley]

I wonder what dyes they are using that give a significant and consistent change of coloration in a narrow range of pH changes. I am assuming that the method relies on adding enough acid to neutralize the maximum KH in the devices range, then measures the pH to determine the amount of remaining unreacted acid. Meaning, the indicator should give a linear response of coloration in the range from zero and up to acidity required to kill the max KH in the range.

Here’s a published method using bromcresol green

https://www.sciencedirect.com/science/article/pii/096706379390149W

 

[vahegan]

Here’s a published method using bromcresol green

https://www.sciencedirect.com/science/article/pii/096706379390149W

Thank you, Randy. I think I have bromkresol green. I can give it a try.

 

[Roli's Reef Ranch]

There is a way to hinder the Hanna alk to show lesser and lesser dKH (or ppm for that matter) with age of open reagent bottle. I had the same story as many have reported here - my reading decrease from a new open bottle with time. Double check with another method show that there was not a real decrease - only that the reagent did not give the colour it should. Comparing with a fresh newly open bottle confirm the false readings of the old reagent. I did a test with shaking the bottle every time I use it - not better result. After this I start to store all open bottles in my refrigerator and voila - it works and give the right readings all the time. I have tested this for 8 months now and comparing with other types of measurements - the last bottle is now 4 months old (open) and still give the same result as my other tests (and a brand new opened bottle)

My findings - Store the open reagent bottle in a refrigerator, shake before use, It works with the cold reagent directly taken from the refrigerator

Other way to handle the test is to always use the same vial, use the same syringe and tip and clean the vale now and then with citric acid

Edit - the period I had tested it - checked my logs - it was 8 months not 6

Sincerely Lasse

I've experienced the same thing with Trident Alk reagent. I'd assume it to be a similar formulation.

 

[vahegan]

https://www.sciencedirect.com/science/article/pii/096706379390149W

So they are using hydrochloric acid, and it is likely that Hanna, as well as most manufacturers of KH monitors are using the same. But hydrocloric acid is very volatile.
Do you think it would be possible to replace it with some dry acid for KH titration? Something like malonic acid, or maybe monosodium sulphate? If we can replace the liquid with a dry reagent, it will have less chances to go bad. The downside is that it is easier to apply an accurate dose of exactly one ml using a syringe. Dosing dry powder with a spoon may bring more variation, and in this type of test we need to be as accurate as possible with the amount of added acid

 

[Randy Holmes-Farley]

Hydrochloric acid is not volatile when it is a concentration like 0.1 M, but sulfuric acid also works fine for titrations.

 

[Lasse]

Update

I open one bottle the 14/5 this year and it had expiration data november this year. Lot 9576- Stored in refrigerator all the time. It was nearly empty and i notice that i was som precipitation in the sample after adding the reagent. I open a new bottle, and confirm that the old was around 0.5 low. Both with KH director and Tropic Marine pro test. So - in spit of store it cold - there could be drifts. But I saw it clearly - it was like a green skin floating in the sample

Sincerely Lasse

 

[uninformed]

Update

I open one bottle the 14/5 this year and it had expiration data november this year. Lot 9576- Stored in refrigerator all the time. It was nearly empty and i notice that i was som precipitation in the sample after adding the reagent. I open a new bottle, and confirm that the old was around 0.5 low. Both with KH director and Tropic Marine pro test. So - in spit of store it cold - there could be drifts. But I saw it clearly - it was like a green skin floating in the sample

Sincerely Lasse

Yes, I have seen the same “green skin” precipitate in some of my past reagent bottles as well. I did not, however, note if those bottles were the ones that read low. I’ll have another data point here in the next week when I open a new bottle.

 

[Reefahholic]

I use mine so quickly that I’ve never had an issue. Although I have had inconsistent batches.

 

[gbroadbridge]

Update

I open one bottle the 14/5 this year and it had expiration data november this year. Lot 9576- Stored in refrigerator all the time. It was nearly empty and i notice that i was som precipitation in the sample after adding the reagent. I open a new bottle, and confirm that the old was around 0.5 low. Both with KH director and Tropic Marine pro test. So - in spit of store it cold - there could be drifts. But I saw it clearly - it was like a green skin floating in the sample

Sincerely Lasse

I have one bottle opened 4 May stored in the fridge at 4C

It has not drifted from initial measurement.

I always shake the bottle before drawing 1ml.

 

[map2022]

It is possible that one of the dyes that Hanna uses is susceptible to air oxidation. That would become more and more of an issue as the reagent in the vial declines (more air/O2 to less reagent) and the cooler temps in a fridge could reduce the reaction rate. It might also be very dependent on batch since air oxidations are often catalyzed by trace metals such as iron.

I always get lower readings from nearly-empty bottles of Hanna alk reagent than from new bottles (last time the difference was a full 3 dKH). I also suspect oxidation or maybe CO2 absorption could be at play, because the effect gets larger as the ratio of air to liquid in the bottle increases.

I think I’ll try transferring a fresh bottle of reagent to a serum vial and using a needle on the syringe to withdraw it through the stopper for each test. That won’t completely eliminate gas exchange, but would limit it to one ml of new air into the vial for each ml of reagent withdrawn.

 

[gbroadbridge]

I always get lower readings from nearly-empty bottles of Hanna alk reagent than from new bottles (last time the difference was a full 3 dKH). I also suspect oxidation or maybe CO2 absorption could be at play, because the effect gets larger as the ratio of air to liquid in the bottle increases.

I think I’ll try transferring a fresh bottle of reagent to a serum vial and using a needle on the syringe to withdraw it through the stopper for each test. That won’t completely eliminate gas exchange, but would limit it to one ml of new air into the vial for each ml of reagent withdrawn.

Why not just put it in the fridge?

That has a 100% success rate as far as I can tell

 

[map2022]

Why not just put it in the fridge?

That has a 100% success rate as far as I can tell

Fair enough. I guess my hang up is that unrefrigerated bottles don’t seem to degrade until they’re opened, so temperature alone doesn’t seem to be the cause. But based on earlier replies about green skin, I guess it could be microbial activity and refrigeration would help that.

 

[gbroadbridge]

Fair enough. I guess my hang up is that unrefrigerated bottles don’t seem to degrade until they’re opened, so temperature alone doesn’t seem to be the cause. But based on earlier replies about green skin, I guess it could be microbial activity and refrigeration would help that.

According to Hanna, the dye oxidises and thus does not show a true color.

Which is why they say 3-6 months life once opened depending on temperature.

 

[fishmonkey]

Does this apply to titration kits like the salifert alk kit?

 

[gbroadbridge]

Does this apply to titration kits like the salifert alk kit?

No, salifert is a simple Hydrochloric acid titration, with a pH sensitive dye that changes color. It does not oxidise.

It is a very good test kit.

 

[tritonpower]

Update

I open one bottle the 14/5 this year and it had expiration data november this year. Lot 9576- Stored in refrigerator all the time. It was nearly empty and i notice that i was som precipitation in the sample after adding the reagent. I open a new bottle, and confirm that the old was around 0.5 low. Both with KH director and Tropic Marine pro test. So - in spit of store it cold - there could be drifts. But I saw it clearly - it was like a green skin floating in the sample

Sincerely Lasse

7 month update. I have kept the bottles in the fridge for the last 7 months. I only do 2 tests/week so it takes me a while to go through a bottle. I have checked with salifert multiple times and have not seen any difference with the hanna checker. I had multiple hanna bottles "go bad" prior to keeping them in the fridge. Like others, working great for me.

 

[Reef.]

7 month update. I have kept the bottles in the fridge for the last 7 months. I only do 2 tests/week so it takes me a while to go through a bottle. I have checked with salifert multiple times and have not seen any difference with the hanna checker. I had multiple hanna bottles "go bad" prior to keeping them in the fridge. Like others, working great for me.

I’m also finding the results are consistent but are a full 1dkh above Salifert, are you finding that the Hanna gives a higher reading than Salifert?

 

[vahegan]

OK, here I am back to confirm that @Lasse 's method of storing the open reagent works for me.

There was little reagent left in the older bottle which I have been using for a few months now. I have got a surprisingly low reading yesterday (and my readings were consistently dropping in the previous couple of weeks, even though I have increased the doser setting for the 2-part addittive), so I wanted to check and opened a new bottle to compare the results. I got only 0.1KH difference.

With my very first bottle, which I kept at room temperature and was only shaking before each use, I recall that there was a more than KH2 (!) difference when I opened the new bottle.

So, storing the reagent in the fridge works great. Thank you, Lasse, for finding this out for us!

Yet another update. I did a test with the remaining "last milliliter" (it was probably only 1.2-1.3ml left in there - certainly not enough for a second test) remaining in the same old bottle, that was kept in the fridge all the time. I got a 7.1KH reading with the old bottle, and 6.5KH with the fresh one. There was only 0.1KH reading difference between the same 2 bottles in July.
My conclusion is, even in the fridge, should not keep the reagent for too long, once opened. Especially when there is very little reagent left in the bottle as it is more likely to oxidize when the reagent-to-air ratio decreases.
I wonder why Hanna has chosen the bottle and syringe method for application of this test. Single use sauchets with exactly 1ml of reagent would be easier to use, and less likely to oxidize in storage. I wonder if I can DIY something like this. For example, pre-fill 25pcs of insulin syringes when opening the new bottle. Then, they can be re-used with the next bottle. I need to think of some way to seal the tips of each syringe ones they are filled, can't thing of other downsides for such approach. And with prefilled syringes, it will further reduce the time of the test.

 

[Lasse]

Yet another update. I did a test with the remaining "last milliliter" (it was probably only 1.2-1.3ml left in there - certainly not enough for a second test) remaining in the same old bottle, that was kept in the fridge all the time. I got a 7.1KH reading with the old bottle, and 6.5KH with the fresh one. There was only 0.1KH reading difference between the same 2 bottles in July.

But in this case - the old was higher

My conclusion is, even in the fridge, should not keep the reagent for too long, once opened. Especially when there is very little reagent left in the bottle as it is more likely to oxidize when the reagent-to-air ratio decreases.

Yes - I have notice that too, Further on - I have forgot to put the bottle into the fridge for x days - and that bottle showing less after that

I wonder why Hanna has chosen the bottle and syringe method for application of this test. Single use sauchets with exactly 1ml of reagent would be easier to use, and less likely to oxidize in storage. I wonder if I can DIY something like this. For example, pre-fill 25pcs of insulin syringes when opening the new bottle. Then, they can be re-used with the next bottle. I need to think of some way to seal the tips of each syringe ones they are filled, can't thing of other downsides for such approach. And with prefilled syringes, it will further reduce the time of the test.

My salinity standard comes in a 25 ml syringe - no problem with standards that change after a while

Sincerely Lasse