Drifting alk reagent?

reeferpat137 · Mar 20, 2023

Went on vacation for 12 days, got home and just tested my alk. Hanna read 8.7 before i left, 11.0 today. Redsea reads 9.2.... i checked the hanna with standard solution, its spot on. I also did a small, maybe 2 gal WC. Fluval 13.5 dosing All For Reef. Should i trust the hanna? Does reagent drift over time?

blaxsun · Mar 21, 2023

Yes (trust, but verify) and yes, reagents are known to drift. With the Hanna you can have all sorts of variances, from the black line being printed at different heights on the vials (use a syringe measurement instead), how clean the vial is, any fingerprints on it, etc. And the reagents can drift. I always like to have a backup titration test kit to keep the Hanna honest.

reeferpat137 · Mar 21, 2023

blaxsun said:
Yes (trust, but verify) and yes, reagents are known to drift. With the Hanna you can have all sorts of variances, from the black line being printed at different heights on the vials (use a syringe measurement instead), how clean the vial is, any fingerprints on it, etc. And the reagents can drift. I always like to have a backup titration test kit to keep the Hanna honest.

I try to be as precice as possible, only using one vile, for as long as i can until the line fades. Filling so that the bottom curve of the water is almost perfect with the line. I even rince the cuvette the same way every time. I try to be very accurate... i do have another bottle of reagent, but i didnt want to open it just to double check. I did notice my Ph was low, 8.0, and found the venturi fitting was partially pluged reducing air flow through my Co2 scrubber. Fixed the air flow and Ph went back to 8.4. Im guessing that reduced Ph will lead in increasing alk levels?

blaxsun · Mar 21, 2023

I know there's some relationship between pH and alkalinity, I just don't recall what it is offhand.

homer1475 · Mar 21, 2023

How long has the bottle of reagent been open?

A small PH (.3) fluctuation wouldn't cause your ALK to rise that high unless consumption changed. I would open the other bottle and verify.

Just had to do this myself. Got an odd reading from my already open bottle, tested again, got the same number. I have several in my cupboard, so I opened a new bottle, and got roughly the same reading. Also used a salifert titration test, and again got the same number. I knew my ALK had jumped, but no idea why, and verified my reading with 2 other test. I would never trust a single data point, and most certainly would never react(shut my doser off for a day or 2 till I'm back in line where I like to keep things), without a second, or even third confirmation.

Remember stability is more important then any particular number.