Which probe should I trust? Apex and Hanna pH probes results differ.

[reefkeeper2]

I recently bought a new pH probe for my Apex and a Hanna Halo 2 pH tester. I bought the Halo as a backup in case I had doubts about the Apex reading and to measure the pH of the water I use for my orchids.
I calibrated the Apex probe and got a reading of 8.11 for my tank. If I take that probe and put it in pH 7 buffer I get a reading of 7. If I put it in the 10 buffer I get a reading of 10. All good. I calibrate the Halo and check it the same way. All good. But surprise surprise the Halo gives me a tank reading of 8.3
So I have two calibrated probes, both of which give accurate readings on the buffer solutions that give significant different readings on my tank. What gives? Which do I trust?

 

[therootcause]

That’s a tough one. Were calibration solutions brought up to tank temp for both sets of cals?

Did you use the same brand/type of buffer for both pieces of equipment?

 

[FishTruck]

8.3 is pretty high for a reef tank.... a great result some would say, but tough to achieve. I'm more suspicious of that one.

You are measuring at the same time both probes, right?

 

[reefkeeper2]

That’s a tough one. Were calibration solutions brought up to tank temp for both sets of cals?

Did you use the same brand/type of buffer for both pieces of equipment?

Yes and yes.

 

[reefkeeper2]

8.3 is pretty high for a reef tank.... a great result some would say, but tough to achieve. I'm more suspicious of that one.

You are measuring at the same time both probes, right?

Yes. I tend to believe the Halo. I am slow dosing a kalk slurry and the reading was taken late afternoon at highest pH.

 

[Randy Holmes-Farley]

Maybe both are wrong. lol

Luckily, both values are fine.

 

[exnisstech]

8.3 is pretty high for a reef tank.... a great result some would say, but tough to achieve. I'm more suspicious of that one.

Just curious why is this.? I run 3 tanks, 2 stay at 8.3 and a third at 8.6. The 8.6 is a larger tank and gets 5400 ml kalk a day over a 24 hr period. The other two get 10 and 15ml 2 part. I do nothing else to effect pH except an airline on the skimmer of the tank in our bedroom due to it dropping to 7.9 over night. 8.3 now with the airline.

 

[reefkeeper2]

Maybe both are wrong. lol

Luckily, both values are fine.

I dose kalkwasser at night which is most of my topoff. During the day I slow drip it, 0.8 ml per minute. When I saw my pH dropping below 8 by morning I got suspicious so I ordered the new probes. I got the Apex probe first and the pH readings where even slightly lower. So I switched my slow drip to kalk slurry. I've done this before usually through the winter when everything is closed up tight. Then the Halo arrived. Now I don't know if I need the kalk slurry or not. Very frustrating.

 

[jda]

You are going to have to pick one to trust. I would choose the Hannah and use it wisely - keeping it calibrated, rinse it off with freshwater after each use, etc.

pH probes are perhaps the weakest link in any tank, so I would not trust them much at all. They fail, drift, etc.

 

[FishTruck]

Just curious why is this.? I run 3 tanks, 2 stay at 8.3 and a third at 8.6. The 8.6 is a larger tank and gets 5400 ml kalk a day over a 24 hr period. The other two get 10 and 15ml 2 part. I do nothing else to effect pH except an airline on the skimmer of the tank in our bedroom due to it dropping to 7.9 over night. 8.3 now with the airline.

Maybe “tough to achieve” was too strong. I would restate… “ if you are not using Kalk or active aeration, and making an effort to raise the pH, I would be more suspicious of the 8.3 value than the 8.11 value.

It would be necessary though to see the diurnal cycle as read by both probes and see if the values ever converge.

I personally don’t put much faith in my pH probes. I gave up using them as control points a long time ago. Like Randy said, both values are acceptable, so I would just pick one probe and forget about the other one and follow trends and goals.

 

[FisheRare]

I recently bought a new pH probe for my Apex and a Hanna Halo 2 pH tester. I bought the Halo as a backup in case I had doubts about the Apex reading and to measure the pH of the water I use for my orchids.
I calibrated the Apex probe and got a reading of 8.11 for my tank. If I take that probe and put it in pH 7 buffer I get a reading of 7. If I put it in the 10 buffer I get a reading of 10. All good. I calibrate the Halo and check it the same way. All good. But surprise surprise the Halo gives me a tank reading of 8.3
So I have two calibrated probes, both of which give accurate readings on the buffer solutions that give significant different readings on my tank. What gives? Which do I trust?

My issues are somewhat similar to yours. i test with my hanna checker ,API and seachem ph testers and get 8.4,8.3 and 8.4 . when calibrating in 7 and 10 buffer solution its accurate but as soon as i put probe back in to sump it drops to 7.6 every time . i cleaned probe numerous times and purchased 2 additional probes and it continues to give me a 7.6 reading when all of my testers are 8.3 and up . could my apex pro be faulty ?

 

[Randy Holmes-Farley]

My issues are somewhat similar to yours. i test with my hanna checker ,API and seachem ph testers and get 8.4,8.3 and 8.4 . when calibrating in 7 and 10 buffer solution its accurate but as soon as i put probe back in to sump it drops to 7.6 every time .

Maybe a ground loop issue?

pH Readings off the Mark? | Murphy & Dickey, Inc.

Symptoms Include: The analyzer reading is offset from the process reading by a consistent amount. The analyzer reading is frozen on one value....

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