Accurate pH meter vs test?

[Zain]

Hey everyone,
This morning I calibrated my pH meter which was originally reading 8.1; and found out my aquarium pH was actually 7.5, I was kind of surprised because I only had to adjust the meter a few points. Anyway, I started adding calcium hydroxide with r/o water and brought the pH up to 7.8 and am still trying to raise it. However, since I was doubting the pH meter, I decided to use a standard test kit. The reading came to be 8.2-8.4. Now this might be obvious, but what should I believe the year old test kit, or my recently calibrated pH meter? If the meter is right, then my pH has been at 7.5 and even lower at times and none of my coral (zoos, mushrooms, LPS) and fish have not shown any signs of irritation. Shouldn't such a low pH have adverse effects on my coral?

 

[TheH]

Clean the pH probe in vinegar for a few hours, and recalibrate with a new set of recent calibration solutions. I think your pH meter is off.

 

[bertoni]

I agree. 7.5 is getting low enough that it might start to kill animals. The calibration standards might be off, too.

 

[oscar.millan]

Calibrate Ph meter again, get a new test kit to confirm results. Low or high Ph isn't usually the problem, drastic drop or climb of Ph usually results in losses.

 

[Boomer]

How old is this pH probe/meter and who's is it ? Who's pH test kit are you using ? The only really good seawater pH test its in this hobby are Instant Ocean and Kordon, as they use Metacresol Purple, which is the same chemical oceanographers use for pH measurement or the determination of P-Alkalinity.