Calibrating a PH Probe

A few days ago I noticed my ph seemed lower than it should be, this was also after adding a CA reactor so I almost thought it was normal. Except I have had my ALK levels at their highest as of lately, which usually raises ph(I repeat usually). 7.9 during the wee hours of night had me curious, not worried because I think a drop to 7.9 at night is acceptable, but curious.

The first thing I did was decided to calibrate my aquacontroller, it's been a few months anyways. I used 4.0 and 10.0 solution. (I always heard I was supposed to use 7.0 and 10.0 or 4.0 and 10.0) either way I used 4.0 and 10.0. My reading jumped from about 8.1 to 8.3, sort of a big difference when it comes to ph.

I let it run through the night still thinking, I wonder which is correct... Today I remembered about the reccomendation to use calibration solution that is 3 units from the other ie 4.0 and 7.0 or 7.0 and 10.0. So I calibrated again this time using 7.0 and 10.0. Before Calibration 8.27, after calibration 8.42. This got me VERY curious again...

I have always questioned how the aquacontroller does it's calculations to get the ph calibrated. MOST other contollers or monitors do not do it automatically you have to go back and forth to and from hi and low solutions until you get it "dialed" in correctly. The Aquacontroller takes one reading from each solution, the comes up with the correct PH. Then I remembered I have one of the manual pinpoint monitors in a drawer.

I pulled out the monitor, plugged in the probe and calibrated it with 7.0 and 10.0. I got a reading of 8.25 in the tank. Only .02 off from what the aquacontroller said when I calibrated it with 4.0 and 10.0. Since both of those are very close to the same number I thought that must be the most correct...

I broke open new packets of 10.0 and 4.0 and calibrated the aquacontroller again, after calibration I got 8.28. Pulled the probe and put it in the ph monitor again, it said 8.25. At this point I have called 8.28 "my tanks ph."

Now, is the difference between having a ph of 8.4 and 8.10 that big of a deal in a reef tank? IMO no, I believe the key is stability. If you have a swing that is less than .2 and your ph is always above 7.9, IMO your tank is fine. But sometimes people get overly stressed out that their ph is 7.9 instead of 8.2, maybe the problem is in your test kit, controller, or monitor. If your tank looks good, feels good, smells good, and tastes good, it's probably good.

I believe some of the people with "ph problems" that are "doing everything right" and still have a "problem", may only have problems with their testing.

Happy Reefing!

 

I totally agree with what you have here and I am guilty of not calibrating my probe often enough. Stability is the trick, I use to have .4 swings in my PH until I added the fuge and did a reverse photo period. I am at 8.2 but afte rthis thread I will calibrate this evening

 

Hope your calibration does not take as long as mine.

 

Nah, to be honest I don't go crazy with it. I'll use a 7 & a 10 solution I have and do each one once and that will be that. But I will do it...that's the good part

 

With the aquacontroller 4 and 10 soloution is used for fresh water and 7 and 10 is used for saltwater. One thing I would be curious about is how old and clean your probe is? How about the pinpoint tester?

Neither one of your readings sound that bad though and you're right, the key is stability.

 

I thought 4 and 7 solution is used for freshwater. I actually thought 4 and 10 is basically never recommended, something about the values being 3 from each other was important for some reason.
The probe is less than 6 months old, and cleaned it with "cleaning solution" before calibrating. The pinpoint monitor is older, maybe two and a half or three years old. I was using the same probe though.

 

I bought big jugs of 7.0 and 10.0 solution to calibrate. I just bought an Aquacontroller Jr, which came with 4.0 and 7.0 solution. I'll keep the 4.0 for storage solution if I ever have to remove it from my system.

 

I talked to Curt from Neptune and he told me to use 7.0 and 10.0 because it is closer to the range you are using. Before I calibrate I drop the probes in solution to see if they read correct. If they do then I don't need to recalibrate unless they are off..

I talked to him because I thought I was having noise issues in my water. He stated that if I ever think I have noise (or gnd problems) I need to test the water say in the sump then take a cup of water and stick the probe in it to see if I get the same readings. If not then start unplugging stuff until I find the problem.

 

That's what I remember otty, that's why I tried that the second time. With the aquacontroller I was getting 8.42 after calibrating with 7.0 and 10.0, but after calibrating the pinpoint ph monitor with 7.0 and 10.0 I was getting 8.25. Thats why i tried one more thime with 4.0 and 10.0 with the aqua controller, which brought me back to 8.28.

I did try to testing water in a cup because of noise issues, same reading.

One more note, if I calibrate with 10.0 and 4.0. All readings are correct 4.0 7.0 and 10.0. When I calibrate with 7.0 and 10.0 Both 7.0 and 10.0 are correct but 4 reads about 4.40.

 

I'll have to try that too because I have about 4 packs of 4.0 still here at the house too. Will try and do it this weekend and let you know what I come up with.

Thanks for the info. ;D