Different Test Kits, Different Readings

prior20

New member
I have a Hanna Checker for calcium and it usually gives me 450-500. I also have a DA reefkeeper pH probe that usually reads about 7.9. I took my water to my LFS today and calcium was like 370 and pH was 8.3. I just moved and am losing a few things so I am trying to figure this out. Don't know which ones to trust. The LFS had API test kits and they were brand new.
 

immortl

New member
Have you calibrated either of your two electronic instruments lately? My understanding/limited experience with these is that you can purchase calibration fluid of known values and you adjust the instruments as necessary.
 

prior20

New member
I calibrated the pH probe when I moved which was about 3 weeks ago and I don't think you can calibrate the Hanna checker. I just did a test with my own API kit and calcium was 400 and pH was closer to 8.3. I will recalibrate the pH probe again.
 

prior20

New member
I just moved my pH probe to a different location in my sump and it is now reading 8.3. Glad I got that one figured out but still worried about calcium. I lost a clam and my two fungia plates are receding a bit.
 

disc1

-RT * ln(k)
pH readings can change drastically in the time it takes to go to the LFS to get checked. So that measurement is useless.

Those Hanna checkers have had some issues with alk and cal. I'd check it against a solution with a known calcium level.
 

brandon429

In Memoriam
When I read that it reinforced all the wrong ammonia tests id seen all those years online...from distilled water, from tanks running soft cycles that had no origin of decay etc
People always think if a test says it, its there, but the predictability of real ammonia readings far exceeds that of any test kit indication.
Knowing test kits are mere range indicators subject to completely wrong readings really helps not to tweak on them too much. If there was a given water param I cared about, id own multiple kits from different companies before taking action.
 
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