pH meter question

[wbholwell]

My pH meter had been reading 8.35 to 8.50 since I came home from being absent all weekend. Suspecting something wrong, I replaced the battery and recalibrated it. After replacing the battery it still read high. It now reads 8.18. Slope accuracy (?) was around 76%.

Is it time to replace the probe?

 

[victor626nj]

probably so sam sells them for about 40 bucks

 

[wbholwell]

No other opinions???

 

[xyzpdq0121]

What is the temp reading? Temp and PH are dependant in most probes, if your temp is off, your PH will be off. What meter are you using?

 

[wbholwell]

My temp stays at a pretty constant 79.5 deg F. It doesn't seem to fluctuate more than <u>+</u> 0.5. My monitor is an ExTech Oyster 10 (I think). It has a temperature setting that is adjustable, and I've set it to match the tank temp. So I don't think that's the problem.

 

[xyzpdq0121]

Hummmm, no spots on the glass part of the probe?

 

[wbholwell]

Spots? I dunno- I'll check tonight.

Link to the meter:

 

[FutureInterest]

Probes go bad over time, I'm not sure how long since I've had the same one for a year and its still on its mark. Don't assume the probe is just broken and buy a new one, even if its just 40 bucks... that's silly cause that's 40 bucks that you might not have to spend.

Don't you have any chemical test kits to check the ph with? If not, take a sample of your water in to get it checked at a LFS. In the alternative you can borrow my spare ph probe or any of my ph test kits.

 

[skriz]

test you cal fluid. If the cal fluid is 7.0 and your ph meter reads anything but, you may have a probe issue.

or, not sure if cal fluids go bad over time. But, I have some fresh 7.0 and 10.0 if you want to borrow them.

 

[xyzpdq0121]

Ya Raj could be right... What are you using for your calibration? I do know that fluid CAN be saved but it WILL go bad over time.. are you using new solution and if so, you mihgt want to spend $2 on new solution just to make sure you did not get a bad sample.

 

[wbholwell]

Thanks for the advice everyone. I recalibrated the meter using calibration fluid pH of 7.01 and 10.01. Before I hit the recalibration button, the readings were about 0.4 too high. After calibration, the meter gave an electrode slope of about 76%. Of course it read exactly 10.00 in the calibration fluid after calibration.

Because the readings crept up over a relatively short period of time, I am thinking the probe is going bad. I'll give it a week and then retest it using calibration fluid. If it's not close to spot on, I guess it's time for a new probe.

 

[wbholwell]

Xyzpdq0121;96224 wrote: Ya Raj could be right... What are you using for your calibration? I do know that fluid CAN be saved but it WILL go bad over time.. are you using new solution and if so, you mihgt want to spend $2 on new solution just to make sure you did not get a bad sample.

I have no idea how old the fluid is- I got my meter used (chicagoman35 ?) and he was kind enough to give me a bunch of packets of calibration fluid. I would think a sealed packet of calibration fluid would last a very long time, though.

 

[mwitten]

wbholwell;96226 wrote: Thanks for the advice everyone. I recalibrated the meter using calibration fluid pH of 7.01 and 10.01. Before I hit the recalibration button, the readings were about 0.4 too high. After calibration, the meter gave an electrode slope of about 76%. Of course it read exactly 10.00 in the calibration fluid after calibration.

Because the readings crept up over a relatively short period of time, I am thinking the probe is going bad. I'll give it a week and then retest it using calibration fluid. If it's not close to spot on, I guess it's time for a new probe.

I am assuming you cleaned the probe (vinegar soak, etc.) right? I did not see the age of your probe, but depending, a year of continuous use is good.

The cal fluids definitely expire and drift. There may be an expiration date on them (if using packets), or you can check the brand website for shelf life info. Also, check the temp compensation... it will impact the calibration standard as well.

Another fun thing is making sure you don't get one standard into the other and change them. I dip in RO/DI water and shake/wipe dry between them, then let them sit int the calibration solution until everything settles (Temp as well).

You can also use Borax to make a standard. Don't have the article handy, but you can search the ARC board for Borax and probably find it. If not, let me know. It is good for a sanity check. Cheap, too...

Good luck!

-Mike

 

[wbholwell]

Thanks for the info, Mike! I didn't clean the probe with vinegar, I just rinsed it well in RO/DI water. If there is no chance of coraline build-up (it's in the sump) is this necessary/beneficial? Also, I'll look for an expiration date on the fluids when I get home. And I did compensate for the fluid's temp. (I set it to the ambient air temp. And of course I did rinse with RO/DI between calibrations.

Thanks!

mwitten;96228 wrote: I am assuming you cleaned the probe (vinegar soak, etc.) right? I did not see the age of your probe, but depending, a year of continuous use is good.

The cal fluids definitely expire and drift. There may be an expiration date on them (if using packets), or you can check the brand website for shelf life info. Also, check the temp compensation... it will impact the calibration standard as well.

Another fun thing is making sure you don't get one standard into the other and change them. I dip in RO/DI water and shake/wipe dry between them, then let them sit int the calibration solution until everything settles (Temp as well).

You can also use Borax to make a standard. Don't have the article handy, but you can search the ARC board for Borax and probably find it. If not, let me know. It is good for a sanity check. Cheap, too...

Good luck!

-Mike

 

[mwitten]

wbholwell;96233 wrote: Thanks for the info, Mike! I didn't clean the probe with vinegar, I just rinsed it well in RO/DI water. If there is no chance of coraline build-up (it's in the sump) is this necessary/beneficial? Also, I'll look for an expiration date on the fluids when I get home. And I did compensate for the fluid's temp. (I set it to the ambient air temp. And of course I did rinse with RO/DI between calibrations.

Thanks!

Well, they do seem to go a lot longer in the sump. Without light there is not much for corraline to work with, but there are other things that can grow on them. To be honest, I just don't know. I have separate probes in my sump I am planning to clean for the first time myself this weekend.

I have actually been planing to build a new probe holder for my display out of black plastic to see if I can extend the time between cleanings... I thought I would build it with a "shade" to keep most of the light off the probes, if I can do it without blocking too much flow.

What type of PH meter or controller (and probe) do you have? It might be interesting to compare how they do with/without that kind of cleaning. Since you plan to replace it anyway, it might not hurt to soak it for 24 hours and see how things change. I'll let you know what I find out as well... I have 2 Neptune "lab grade" for my continuous monitoring in the display and sump.

-Mike

 

[wbholwell]

Yeah, I may try soaking it in vinegar. But it seems to be doing fine so far- we'll see when I check it in a few days. And here's a link the to meter & probe that I have.