Testing help. What alkalinity am I at?

[Schulks]

I have been testing a lot lately because I am using All-for-Reef on a doser now. I am using an old Salifert alkalinity kit that I have had well over a year but it expires in 2027. I am also using a new Hanna Alkalinity checker which has really surprised me with how repeatable the results are. I am using both to test and Salifert always comes within +/- 0.1 of the Hanna. I use the Hanna numbers as record because it tests the same back to back to back. My alkalinity started at 7.0 and I have raised it to 7.6 over about 10 days.

Last night I opened up a new Hanna reagent and a new Salifert Alkalinity kit. The Old kits and New kits both line up but not with each other. The old Hanna reagent and old Salifert tested 7.5. New Hanna and new Salifert tested 7.8. New tests are up 0.3 dkh.

Then I dosed some more red sea B to continue raising alkalinity.

Today old Hanna tested 7.6 - expected - New Hanna tested 7.9. Still up 0.3 dkh - Consistent results between the bottles for what I expected it to raise.
Old Salifert 7.7 New Salifert 7.85. Which is still roughly lining up.

What number would you believe is the alkalinity?
Hanna is being consistent so I'll continue to use it but should I go with the 7.6 or 7.9? I'm going to test again later tonight with all 4 and then probably toss out the old ones.

 

[Formulator]

There is not really a great way to say for sure, but I’d tend towards the new value. Practically speaking it doesn’t really matter. I would just take the new value as your new baseline and continue to strive for stability around that value. If there was a bigger difference between the two, maybe I’d investigate further, but IMO not worth the dive down the rabbit hole for this small difference.