Another PH Dilemma

[flyfisher2]

I recently acquired an Apex and I'm having a bit of a problem. For the last couple years I've tested my PH with Salifert, API, Red Sea Test kits. As one of the easier test to perform I would usually get a reading between 7.9 and 8.1
I set up the Apex a few days ago and immediately noticed the PH to be in the 7.5 to 7.6 range. I recalibrated manually several times and still came back with the same numbers. I tested the same sample at the same time with my existing Salifert and a new box I just opened in addition to the API. All three came in around 8.0.
I have since contacted Neptune and they promptly replied and requested I do a manual recalibration. I used my last two pouches of regent and performed the test as requested and provided them with the results after each step. They determined that the probe was in fact accurate based on the readings of 6.99 at 7.0 and 10 at 10.0.

I was asked to verify the Salifert with the same regent. I did so with the 7.0 and I thought the result reflects accurately.
In any case I'm torn here. It's difficult to put aside 3 independent test kit results over one probe result. I forwarded the last pic to Neptune showing that the Salifert was very close to the 7.0 regent. The Neptune agent disagrees and feels the image "looks more like 7.4 and 7.7"
Thoughts, ideas, recommendations?

 

[lulubap]

Not sure how reliable API pH test kits are, so I'd take it with a grain of salt. Last test looks like a hard 7.4. Do you have a LFS you could cross check with? Trying to give my two cents on this thread as it seems like it's a bit empty lol

 

[ZombieEngineer]

Real easy way to check. Make a 0.1 molar solution of baking soda (8.4 grams per liter) let it fully dissolve and check that with the probe. It should read real close to 8.3. If it doesn't either your calibration had some bubbles or contamination (it is imperative to rinse with rodi and wipe dry with a paper towel in between the tank and the solution or between solutions), you got expired or poorly stored calibration solution (if it freezes its garbage), or you got a bunk probe with a non-linearity error.

 

[flyfisher2]

Not sure how reliable API pH test kits are, so I'd take it with a grain of salt. Last test looks like a hard 7.4. Do you have a LFS you could cross check with? Trying to give my two cents on this thread as it seems like it's a bit empty lol

Agreed on the reading of 7.4. The yellow seems a little deeper yellow than the card color. Certainly not greener. Thanks for your input.

 

[flyfisher2]

Real easy way to check. Make a 0.1 molar solution of baking soda (8.4 grams per liter) let it fully dissolve and check that with the probe. It should read real close to 8.3. If it doesn't either your calibration had some bubbles or contamination (it is imperative to rinse with rodi and wipe dry with a paper towel in between the tank and the solution or between solutions), you got expired or poorly stored calibration solution (if it freezes its garbage), or you got a bunk probe with a non-linearity error.

Thanks for that recipe. LOL
I'll get on it as soon as dinner is over.

 

[lulubap]

Agreed on the reading of 7.4. The yellow seems a little deeper yellow than the card color. Certainly not greener. Thanks for your input.

I'm only sorry I can't help more. Just trying to keep this thread alive so you and I can learn

 

[flyfisher2]

Real easy way to check. Make a 0.1 molar solution of baking soda (8.4 grams per liter) let it fully dissolve and check that with the probe. It should read real close to 8.3. If it doesn't either your calibration had some bubbles or contamination (it is imperative to rinse with rodi and wipe dry with a paper towel in between the tank and the solution or between solutions), you got expired or poorly stored calibration solution (if it freezes its garbage), or you got a bunk probe with a non-linearity error.

I did rinse in RO/DI and also dried between each individual test. The solutions were stored but one was brand new as it came with the Apex and all were in the same ball park.

 

[flyfisher2]

I'm only sorry I can't help more. Just trying to keep this thread alive so you and I can learn

I appreciate your effort. Thanks again.

 

[flyfisher2]

I did rinse in RO/DI and also dried between each individual test. The solutions were stored but one was brand new as it came with the Apex and all were in the same ball park.

Based on your recommendation the 8.4 grams is a weight measurement is it not? No way to do this based on volume?

 

[ZombieEngineer]

Based on your recommendation the 8.4 grams is a weight measurement is it not? No way to do this based on volume?

Not terribly accurately. 1/2 teaspoon weighs 3 grams. So you could get close if you leveled the spoon then shook off a little bit beyond level.

 

[flyfisher2]

Not terribly accurately. 1/2 teaspoon weighs 3 grams. So you could get close if you leveled the spoon then shook off a little bit beyond level.

I found a kitchen scale and made the mix Came back at 8.21 Pretty close in my opinion. Will now check the two Salifert test kits and the API

Real easy way to check. Make a 0.1 molar solution of baking soda (8.4 grams per liter) let it fully dissolve and check that with the probe. It should read real close to 8.3. If it doesn't either your calibration had some bubbles or contamination (it is imperative to rinse with rodi and wipe dry with a paper towel in between the tank and the solution or between solutions), you got expired or poorly stored calibration solution (if it freezes its garbage), or you got a bunk probe with a non-linearity error.

 

[flyfisher2]

Okay so tested with probe and came back with 8.21 reading
Tested both Salifert PH kits and the API and here are the results.

 

[flyfisher2]

And here is the PH in tank with probe.

 

[flyfisher2]

And here is the PH in tank with probe.

This leaves me right where I started?

 

[flyfisher2]

Seems too close to call for my eyes.

This leaves me right where I started?

 

[ZombieEngineer]

If you take a cup of tank water and measure it outside the tank, does the reading change?

If not, your apex is at least accurate to within 0.1pH.

If it does, you may have something inducing stray voltage, which is often but not always means you are just about to introduce lots of copper from a failed component in your tank.

 

[flyfisher2]

If you take a cup of tank water and measure it outside the tank, does the reading change?

If not, your apex is at least accurate to within 0.1pH.

If it does, you may have something inducing stray voltage, which is often but not always means you are just about to introduce lots of copper from a failed component in your tank.

Will check right now

 

[flyfisher2]

Will check right now

Same exact reading.
7.56

 

[flyfisher2]

Same exact reading.
7.56

 

[flyfisher2]

So accurate to

Will check right now

so accurate to .1 means?
What is the tank PH ?
Is it 7.56 or 8.0?
Who do I go by?