Testing pH with meter vs. Phenol Red


LifeTime Supporter
Platinum Supporter
Jun 2, 2012
Louisville, KY
I have a Hanna pH electronic meter from my reef tanks days. You stick the thing in the water and and two electrodes measure. Was some 70 bucks, supposed to be **** accurate.

Problem is it reads .1-.2 HIGHER pH than phenol red test kit from K-2006 and the HTH kit from walmart. Tonight K2006 kit said 7.5, pH meter said 7.7.

What to believe? I know the phenol test is about as simple as it can be, but I'm confused about the wide difference.

Could the free CL- ions be messing with the electronic meter? Doesn't make sense. I'm using trichlor tabs for now but really want to get a full handle on what my water is doing. Test results via K-2006:

FC -7
CC - 0
ALK - 100 (using thrichlor tabs for now via chlorinator, want them to up CYA)
CH - 180

MODS - if you want to move this somewhere else, feel free to do so.


Mod Squad
LifeTime Supporter
Platinum Supporter
TFP Expert
In The Industry
Apr 1, 2007
Sebring, Florida
I have never owned one but the consensus on the forum is that pH meters need expensive re calibration from time to time and generally, are not worth the money. Trust your phenol red test.