Alkalinity on 3 different mediums..... and none match

[Qckslvr]

I am sure this is beat to death... But yeah

Last night I scored a great deal on a Hanna Master test kit. I was pretty excited, and have had some shocks... First was Ammonia, it freaked me the eff out when it came up at .1 for both of my tanks. But some research, and some math I learned that my tanks are at about .003

but the one that has me scratching my head is Alkalinity. I did the test 5 times because.... it was just baffling me.

HM first two tests were 9.9! (I then read the bottle, it was expired by 8 months)
HM third test with nice non-expired regent 9.2
Hanna Handheld came up 8.8
API test kit (for giggles) 8.0

I know a while ago when I first set up my 30 I was getting my water tested at Neptune on their fancy tester. I learned that the discrepancy between the their tester and the Hanna handheld was about .4. Their tester read higher than the Hanna.

I am trying to maintain 8.4 for my tang, and other fish that are sensitive to higher alkalinity.

Or am I just chasing my tail on this?

All the other tests on the HM match my handheld, and manual tests pretty damn close.

 

[tribbitt]

Hanna master with non-expired and Hanna handheld seem to agree it's around 9.

Really, pick a testing option and just follow that. A tank can run at 6dkH and be fine, or at 12dkH and be fine. Consistency matters more.

Ask @Thales, he spent a long time trying to measure salinity "properly" and tore his hair out because nothing lined up. Just pick a test and stick with it, pick a target range and stick with it, and you'll be okay

 

[Blaise006]

Worth noting that visually using titration for alk can lead in an overshoot because you don’t know your stopping point which should be between 4.2-4.5 for the acid. I personally don't trust api, but finding the correct stopping point for a proper titration will likely yield closer results to hanna.

I am also not saying the following is the case or that I have performed any test, but if a sample sits between tests, my suspicion is that the ph of that o water sample likely shifts a small amount from the environment or us breathing near it. I suspect this leads to small discrepancies of .1-.3. Probably could be easily verified if someone took a water sample and threw a ph meter in it then breathed near it for 5 minutes to see there is any change.

 

[RandyC]

Hanna Master tester and the Hanna Alkalinity Checker (HI772) both have an error range of ±0.3 dKH ±5% of reading. So you could technically be off by 0.6 dKH between the two testers and still be have correct readings from the devices. Not to mention, you have to throw in some potential for human error.

API is not very accurate at all. I wouldn't bother with API unless you're cycling a new tank, then the ammonia, nitrite and nitrate testers are okay for guidance on the progress of your tank cycle. Also, aquaspin (the fancy tester) at LFSes is notoriously known for giving wild results. Wouldn't trust that tester either.

As @tribbit said, pick one tester and roll with it. The Hanna Master tester will get you close enough. As long as you're within a reasonable range of dKH (6-10), you're better off keeping alkalinity stable and within a smallish range throughout the day than chasing which testers gives you the best result.