pH probe reading low

[clsanchez77]

I have an AquaController Jr. with the pH probe and the pH probe is reading about 0.5 units low. It has been doing this since I purchased the probe back in January. I figured there was a break-in period but it never happened. The probe has been callibrated 3 times and it never makes a difference in the readings.

The probe reads around 7.7-7.8, in both fresh made saltwater and in my tank water. I have used the colormetric tests and confirmed that the pH is in the 8.2-8.3 range.

I meant to contact you sooner but between being relocated with work and the hurricane and my wedding, I am just getting to it.

Please advise.

Thanks, Chris

 

[clp]

Here are some things to check/do:

- Only use single use pH calibration packages. The bottles can be very inaccurate.
- After calibration check with the controller in the run display, check it reads 7.0 in the 7 solution, and 10.0 in the 10.0 solution.

Curt

 

[clsanchez77]

I only use the single use packages, I have the 4.0. 7.0 & 10.0. I know the 7 & 10 is all I need but I wanted to try the 4 to see if there was any difference.

I will recallibrate tonight as I do not remember the exact numbers, it was two weeks ago right before my wedding. What I can remember was the 7.0 callibration fluid was read around 7.8 during callibration and the 10.0 callibration fluid was around 10.6 likewise. I tried to re-read the fluids after callibration and it was not exact, but I do not remember the numbers.

I will report back tonight with current numbers if needed.

Chris

 

[clsanchez77]

Calibration fluids read ok...

Calibration fluids read ok...

Curt:

I recalibrated with 7.0 & 10.0 fluids and checked the pH of the solutions.

The 7.0 & 10.0 callibration fluids are read perfectly. The 4.0 solution is read slightly higher, around 4.05, but then I expected that.

The tank water is still read at 7.75-7.85. Again, I checked this with Seachem and the pH measures to 8.2. FYI, I made a batch of fresh salt-water and it measured at 7.8.

I am concluding that the pH probe is not deffective but rather experiencing interference, either electrical or chemical. What items would cause interference with the pH probe?

I currently have the AC Jr. temp compensation 'on', should I have it 'off'?

The pH probe and temp probe are located about 6 inches apart, is this good?

They are located between two baffles where the water flow is relatively highest in my sump, is this prefered? I figured any of the compartments would be too stagnant.

I have a titanium ground probe in my return pump, Mag 7, chamber. I have a Mag 3 and Mag 7 in the middle chamber for chiller and chemical filter, the baffle with the two probes is in between these two chambers.

I am using Seachem salt, which I understand is slightly higher in borate alkalinity. This, however as I understand, should not effect pH. Are there other elements that would interfere?

Again, using a pH color test, I am reading 8.2, which is expected.

Thanks,
Chris

 

[-=DieselDave=-]

Did you use PinPoint Calibration solution??

I have just started using them and they seem to be off from the other fluids that I have used by about - 0.3, Lot 2510170 on the 7.0 and lot 2508003 on the 10. I'm not sure if they are off or the old solutions are off or my ph in both of my tanks (one with a sump outside) are both reading are 7.9 - 8.0 this is after calibrating two different meters with these solutions.

 

[clp]

Inaccurate calibration solution could certainly cause the problem, but I have not see the single use packets that were that inaccurate.
Try putting the probe in a cup of tank water all by itself and see if it reads the same. Shut off all equipment around your tank. If the probe reads the same it is not interference. There should be water flow where you place the pH probe, but it does not require high flow to be accurate.
What is the alkalinity of your tank? What are you daily pH swings? Are you using a calcium reactor? It could be your pH is much lower than you think. Color matching test kits can be quite inaccurate.

Curt

 

[clsanchez77]

Did you use PinPoint Calibration solution??

I have just started using them and they seem to be off from the other fluids that I have used by about - 0.3, Lot 2510170 on the 7.0 and lot 2508003 on the 10. I'm not sure if they are off or the old solutions are off or my ph in both of my tanks (one with a sump outside) are both reading are 7.9 - 8.0 this is after calibrating two different meters with these solutions.

Inaccurate calibration solution could certainly cause the problem, but I have not see the single use packets that were that inaccurate.

Yes, I used the pinpoint callibration fluids, the single use packs as discussed above. I will check the lot numbers, a 0.3 error would certainly be culprit.

Try putting the probe in a cup of tank water all by itself and see if it reads the same.

I have checked the pH of fresh saltwater with the same result, still in the mixing buckett. I will try it in a cup to verify the same result.

Shut off all equipment around your tank. If the probe reads the same it is not interference.

I have all equipment in the sump off during the 'feed' cycle and the pH does not fluccuate any, so I am ruling out interference from equipment.

There should be water flow where you place the pH probe, but it does not require high flow to be accurate.

I think I have that by having it in a baffle.

What is the alkalinity of your tank? What are you daily pH swings? Are you using a calcium reactor? It could be your pH is much lower than you think. Color matching test kits can be quite inaccurate.

Alk is about 4.5meq/l. The tank is still new and cycling, so Alk demand is minimal at the moment and being maintained with water changes.

I am dripping kalk water into the return chamber, so the probe does not see this as the probe is located before the return chamber. No, I am not using a calcium reactor.

I agree the color matching kits are inaccurate, I only have them to verify the probe. However, reading the pH of new saltwater also being 7.8, I am at a loss.

I think my next step will be to find someone nearby with a pH probe that I could have come over and take some readings.

Chris

 

[atkinsg]

I'm guessing that your pH is low due to excess CO2. Put some tank water in a cup and put the cup outside, preferably with some aeration. Check the pH of the water in the cup after a couple hours. If the pH goes up, you have a CO2 issue.

 

[clsanchez77]

Thanks atkinsg,
I will do the test tonight. How would I correct such as issue?
Chris

 

[atkinsg]

It is caused by a buildup of CO2 in your house. Some people just open a window in the room with their tank and it seems to help. Since my tank is in my basement office with no windows, I had to pump outside air into my sump using an air pump. If you have a skimmer that uses air induction you can run the air hose from the skimmer to outside. So I guess the trick is to somehow get outside air into your tank.

 

[clsanchez77]

My pH is now reading 7.7-7.9, some improvement.

CO2 build-up is the best answer yet but I am not sold on it. I set a cup outside last night and the pH read 7.95 this morning, the same pH my tank reads at its high points.

I am in a condo it that would be impossible to bring in outside air. The tank is situated in my front room whcih has no windows, just a front door.I dont have anywhere to set an airpump and run tubing to the tank.

I will give it some thought however and see if I can not come up with something.

Also, my tank is completeing its cycle this week and I will have one final water change. After that, I will start raising my alkalinity to see if it helps.

Chris

 

[clsanchez77]

This may be a stupid question but I'll ask anyway...

Would low salinity yield low pH, since all the other parameters would be in lower concentration?

Reason I ask, with my ongoig cycle, I have been mixing my water changes batches to 1.023 as opposed to 1.026. This was unintentional and has lead to lower Calcium & Magnesium levels.

I will be rasing the SG to 1.026 over the next few days, would I expect to see an increase in pH along with this as Alk should also increase?

Chris

 

[clp]

I don't think low salinity will cause the low pH. The ion ratios will still be correct, and if the alkalinity is normal, then the pH should be in the 'normal' range.

Curt

 

[clsanchez77]

I aerated the water both outside and inside with slight rises in pH, but still nothing above 8.0. Clearly this is a global warming issue.

I just completed my last large water change so I will begin supplementing the alkalinity and bump it little by little and note the pH changes.

I am hoping that the cycle is complete will help a little. Alk is still at 4 however, so I will bump it to 5, then 6. I am hesitant to maintain anything higher than 6 though.

Chris

 

[clsanchez77]

Tested alkalinity last night and found it to be 3 meq/l. I added enough Carbonate Supplement to raise alk by 1 meg/l to 4 meq/l. pH is now reading in the 7.75-8.00 range.

Will retest and supplement again tonight.

It appears my first alkalinity test was not working properly but my new one is.

Chris