Still problems with pH (and now temp) readings

[Armando]

The phone support hours conflict with my work schedule so I'll try to resolve this here.

So after I got the pH and ORP readings correct from previous thread now I am having problems with pH and temperature.

Last night the pH reading dropped from 8.0 to 7.4 and stayed in the 7.4 range. This morning I calibrated the pH probe but didn't help much, I'm still getting 7.4-7.5 reading. After I was done calibrating the pH, the temperature reading dropped from 79 to 76.

How can this be fixed? I read the FAQs on your site and it mentions some problems with serial cable causing incorrect pH and ORP readings. I unplugged the serial cable and the power adapter for a while but the temp and pH readings didn't change from 76 and 7.5.

I have the pH and ORP probes far apart (one in the sump and one in the tank).

Help?

 

[clp]

Following calibration did the pH read 7.0 in the 7.0 cal solution, and 10.0 in the 10 cal solution? If not, then the probe is not properly calibrated. If so put the pH probe in a cup of your tank water. Is the reading the same?
Are the temperature fluctuations correlated with some device going on or off? The temperature probe can be placed anywhere; it does not have an positional requirements relative to the other probes.

Curt

 

[Armando]

during calibration, I got readings of 7.3 and 10.3. is it automatically adjusted?

the temperature reading on the AQ display dropped right after i did the pH calibration. It remained in 76 afterwards (although my other thermometers tell me 79-80).

 

[clp]

Yes, the AquaController automatically adjusts the calibration constants at the end of the calibration procedure. After calibration with the AquaController in the 'run' display, the pH should read 7.0 and 10.0 in the appropriate solutions.
I recommend calibrating the temp probe to a known standard, and then check that it stays consistent. Perhaps the calibration offset was adjusted previously.

Curt

 

[Armando]

So what should I do to fix the problem with the pH readings? I believe I did the calibration procedure correctly.

 

[clp]

Did the AquaController read 7.0 and 10.0 following calibration? Without doing this test I don't know if the unit is in proper calibration.

Curt

 

[Armando]

OK i re-calibrated the pH, and now it reads 7.0 and 10.0. However when i place the probe in the tank it reads 7.8. I tested the tank with my Pinpoint pH Monitor and it reads 8.15.

Also the temperature on the display quickly switches values in the range of 77 to 79. The temperature with a digital thermometer and the medusa reads 80.

I'm very frustrated

 

[clp]

Did you also calibrate the pinpoint monitor? Does it read 7.0 and 10.0 correctly. If you put the pH probe in a cup of your tank water do you get the same reading? If you unplug the serial cable do you get the same reading? What brand probes are you using?
Are the temp. flucuations correlated with some appliance being on? Is the temp cord routed next to an electronic ballast cord?

Curt

 

[kattner]

From the posted screen shots, doesn't temperature compensation need to be checked for the pH probe set up? Mine is checked and it works fine. The pH readings sound about right since the conditions report show them dropping somewhat at night. The pinpoint probably needs calibrating.

 

[Armando]

Curt,

>Did you also calibrate the pinpoint monitor? Does it read 7.0 and 10.0 correctly.<

Yes, and yes.

> If you put the pH probe in a cup of your tank water do you get the same reading?<

Similar

> If you unplug the serial cable do you get the same reading?<

Yes, but it changes later

> What brand probes are you using?<

The ones that came with the Marine Depot Aquacontroller II deluxe kit.

>Are the temp. flucuations correlated with some appliance being on? <

Doesn't look like

>Is the temp cord routed next to an electronic ballast cord<

It was. I moved it to another location but the temp was still low and oscillating.

So I moved the temp and pH probe to another location, cords far from ballast cords. Readings were still oscillating. I removed the serial cable from the AQ and waited a couple of hours. After this the temp and pH seem stable. pH seem correct. Temp was low so I manually adjusted to the right value.

I ordered the ground isolated serial plug (more $50 ) so I can reconnect it to the computer.

Anything else I should try?

 

[clp]

If you are going to have the serial cable always connected between your AC2 and your PC, then we definitely recommend the isolator. It will prevent the ground loop you are seeing and result in accurate probe readings.

Curt