Question on varying alkalinity test results

russell.dexter · Jan 17, 2025

Looking for some feedback on varying alkalinity results that I can’t reconcile.

Back story is I use Hanna alkalinity tester and KHG auto tester to test alkalinity on my 40 gallon breeder.

I consistently test 8.3 - 8.6 on both devices. (KHG tests every four hours automatically and I reconfirm with a manual test with the Hanna checker twice weekly) Because there is no LFS locally I usually take tank samples when I fly out of the area to have them tested. What’s odd this time is that I had the water tested at two LFS- one with a spin disk and the other with what I think was ATI reagent - both times they advised that my alk was sitting between 11-12dKH. Obviously this is concerning as that’s well out of the range of what I am testing at home.

I can monitor the KHG remotely and have confirmed it is still testing between 8.3-8.6 with the addition of 800mls of kalkwasser daily. I will also pick up some new Hanna reagent and a salifert test kit before I head home and plan to just leave things as they are for the time being.

I figure even if the test result of 8.5 ish is truly 11.5ish it should be fine until I get back home and retest with my new kits.

My question is - is there anyway possible for something to have made my water sample change in transit? I don’t think so because we send icp test off all the time which take far longer to make it to the lab, correct? Total time between collection and testing was 48 hours. This is the first time I’ve seen such a huge discrepancy with my tests.

Thank you for any feedback !

BryanM · Jan 17, 2025

Don't know the answer, but have you done the dKH calibration on the KHG? I know my guardian test results are low, and there's a way to adjust that, assuming you believe your test kit(s).

I might consider stopping dosing, or dosing far less, while you figure out what your ALK is really at... but 11.5 is generally fine.

russell.dexter · Jan 17, 2025

Yes I did do the calibration on the KHG. I also recently (one - two weeks) started a new vial of reagent for the hanna and did not notice any difference between the last few tests of the old bottle versus the ones in the new. Now to be fair I did calibrate by reverse calibration to the Hanna a month or two ago. Unless for some reason I have two 'bad' batches of reagent. Or perhaps I have been testing incorrectly. (Although there is no test easier than the hanna IMO. lol)
Until I get off of vacation and can re-test the water with my new test kits though I figure not to fiddle with the dosing as long as my KHG keeps giving me similar results. I figure even if it's off by the 3dKH consistency might be better than me trying to adjust my dosing from 600 miles away and something going really, really wrong

It's just odd!

BryanM · Jan 17, 2025

russell.dexter said:
Yes I did do the calibration on the KHG. I also recently (one - two weeks) started a new vial of reagent for the hanna and did not notice any difference between the last few tests of the old bottle versus the ones in the new. Now to be fair I did calibrate by reverse calibration to the Hanna a month or two ago. Unless for some reason I have two 'bad' batches of reagent. Or perhaps I have been testing incorrectly. (Although there is no test easier than the hanna IMO. lol)
Until I get off of vacation and can re-test the water with my new test kits though I figure not to fiddle with the dosing as long as my KHG keeps giving me similar results. I figure even if it's off by the 3dKH consistency might be better than me trying to adjust my dosing from 600 miles away and something going really, really wrong

It's just odd!

my KHG reads low, so I used that calibration to align it with the hanna... Thats why I asked.

russell.dexter · Jan 17, 2025

Mine did as well from when I first set it up. I have always calibrated it to the hanna checkers.

Thanks again for the feedback

gbroadbridge · Jan 17, 2025

russell.dexter said:
Looking for some feedback on varying alkalinity results that I can’t reconcile.

Back story is I use Hanna alkalinity tester and KHG auto tester to test alkalinity on my 40 gallon breeder.

I consistently test 8.3 - 8.6 on both devices. (KHG tests every four hours automatically and I reconfirm with a manual test with the Hanna checker twice weekly) Because there is no LFS locally I usually take tank samples when I fly out of the area to have them tested. What’s odd this time is that I had the water tested at two LFS- one with a spin disk and the other with what I think was ATI reagent - both times they advised that my alk was sitting between 11-12dKH. Obviously this is concerning as that’s well out of the range of what I am testing at home.

I can monitor the KHG remotely and have confirmed it is still testing between 8.3-8.6 with the addition of 800mls of kalkwasser daily. I will also pick up some new Hanna reagent and a salifert test kit before I head home and plan to just leave things as they are for the time being.

I figure even if the test result of 8.5 ish is truly 11.5ish it should be fine until I get back home and retest with my new kits.

My question is - is there anyway possible for something to have made my water sample change in transit? I don’t think so because we send icp test off all the time which take far longer to make it to the lab, correct? Total time between collection and testing was 48 hours. This is the first time I’ve seen such a huge discrepancy with my tests.

Thank you for any feedback !

I would trust your own kits over an LFS test.

LFS are normally in a hurry and their tests are conducted for the most part by unskilled operators. Also, Spin tests are notoriously inaccurate.

There are biological processes that can alter Alkalinity, but I would not expect anything measurable by normal tests.

Keep in mind as well, that ICP does not measure Alkalinity, the labs who attach that information to ICP results are measuring Alkalinity by another method or perhaps by calculation.

With a pH meter and a strong acid you can measure Alkalinity accurately at home, but the process is a little involved.

I use this method if I need to test accuracy of other tests.
This is in fact how automated devices such as kh keeper work.

http://www.reefedition.com/a-diy-alkalinity-test-by-randy-holmes-farley/

Randy Holmes-Farley · Jan 17, 2025

russell.dexter said:
Looking for some feedback on varying alkalinity results that I can’t reconcile.

Back story is I use Hanna alkalinity tester and KHG auto tester to test alkalinity on my 40 gallon breeder.

I consistently test 8.3 - 8.6 on both devices. (KHG tests every four hours automatically and I reconfirm with a manual test with the Hanna checker twice weekly) Because there is no LFS locally I usually take tank samples when I fly out of the area to have them tested. What’s odd this time is that I had the water tested at two LFS- one with a spin disk and the other with what I think was ATI reagent - both times they advised that my alk was sitting between 11-12dKH. Obviously this is concerning as that’s well out of the range of what I am testing at home.

I can monitor the KHG remotely and have confirmed it is still testing between 8.3-8.6 with the addition of 800mls of kalkwasser daily. I will also pick up some new Hanna reagent and a salifert test kit before I head home and plan to just leave things as they are for the time being.

I figure even if the test result of 8.5 ish is truly 11.5ish it should be fine until I get back home and retest with my new kits.

My question is - is there anyway possible for something to have made my water sample change in transit? I don’t think so because we send icp test off all the time which take far longer to make it to the lab, correct? Total time between collection and testing was 48 hours. This is the first time I’ve seen such a huge discrepancy with my tests.

Thank you for any feedback !

If the sample had calcium carbonate particles in it (say, from stirred up sand) will give a false high value in any alk test.

russell.dexter · Jan 17, 2025

Thanks a lot Randy for the link to the DIY alkalinity test.

Your comment about calcium carbonate particles gives me pause - I had used some of KZ’s coral snow very late the evening before I took the sample - the water appeared clear very early that morning but perhaps it threw off the test…

I’ll definitely recheck with multiple test kits (and your DIY test) when I get back home to the aquarium.

Appreciate your time !

Randy Holmes-Farley · Jan 18, 2025

russell.dexter said:
Thanks a lot Randy for the link to the DIY alkalinity test.

Your comment about calcium carbonate particles gives me pause - I had used some of KZ’s coral snow very late the evening before I took the sample - the water appeared clear very early that morning but perhaps it threw off the test…

I’ll definitely recheck with multiple test kits (and your DIY test) when I get back home to the aquarium.

Appreciate your time !

Yes, that's a no no for subsequent alk or calcium testing. :)