Problems calibrating pH probe

[HomerJ]

Hi all:

Is anyone else having problems calibrating their pH probe on their ReefKeeper?  I'm up to date with all the software, but the bloody numbers never stabilize.  You're supposed to wait "a few minutes" for the numbers to stabilize, but mine keep going down, and down, even after 30 minutes.  I am sure my pH 7 raw value will end up at 0 if I let it go for another 15 minutes.

I love the ReefKeeper for control of outlets and reading the state of float switches, but I'm kind of losing faith in it's abilities to proper read temperature and pH.  (I also found that my temp probe was 3-4 degrees offset by comparing with other thermometers).

Digital Aquatics are not too helpful in their forums, and getting a hold of them on the phone is like trying to find a parking spot at the mall on December 24.

Thanks!

[NanoSF]

Yes I have to agree with everything you said. It might be a case for both of us that we need new probes, but I don't have faith that this will really fix the problem.

I first got my RK2 used and the probe calibrated as expected. Took about 30 seconds to stabilize. Then I upgrade to the newest version two days later and had to recalibrate. It did exactly what you are saying. It took 20 minuted or so to stop. Now my readings are .3 lower overall. I don't think my PH dropped all of a sudden like that so the probe or unit is wrong. I wonder if it had to do with the upgrade. Did you upgrade before this happened? I mean it was two days after a previous successful calibration. How could the probe fail after two days. Makes me think it is the unit/software.

[redbelly]

Put in a null plug and check your pH value.

If you put in a null plug and the value stays rock solid on you controller then the problem is the probe.
If the values continue to wander then its the controller.

Ph probes typically only last a year at best. I have seen them last 3 years but I have also seen them last 6 months. It really depends on the condition in which they are kept.

You may have a sluggish probe. AKA it takes a long time to react  and a simple cleaning may help. Try the plug first though.

[HomerJ]

Put in a null plug and check your pH value.

Where does one get said null plug?  Is it just a 50 ohm terminator like on the old coax network cables?  The probe is only 4 months old.

[redbelly]

I think a null plug just shorts the 2 terminals out, but dont quote me on that.
But I believe I read somewhere at one time that you can just take a piece of copper wire and it will have the same effect.

Was the probe tip still wet when you purchased it or was it dry?

[HomerJ]

I think a null plug just shorts the 2 terminals out, but dont quote me on that.
But I believe I read somewhere at one time that you can just take a piece of copper wire and it will have the same effect.

Was the probe tip still wet when you purchased it or was it dry?

Yep, the probe came with that little compression thingie containing what I assume was storage fluid.

[NanoSF]

Yes mine was stored wet too. My readings don't fluctuate or take a long time to stabilize now that it is always in the tank. The reading are just low now. What happened after you calibrated HomerJ? Did it fluctuate once in the tank? Or are the readings just incorrect (like my case where they are just low)? I know that a connection to a computer for the MyReef program can make the reading fluctuate. There is some kind of feedback (I don't know the technicalities of this) from the computer that can mess up the PH and Temp probes.

[HomerJ]

Yeah, mine reads low now... if I trust my test kit that is.

[NanoSF]

What controller do you have? If it is RK2 did you also upgrade to the newest version (2.5 I think it is)? I still wonder if the upgrade had something to with it.

[HomerJ]

I have a Reef Keeper Elite.

[redbelly]

I am not sure if it does, but the RK should adjust ph according to temp. Ph is a function of temp. Does your test kit take this into account?

What if you use your calibration fluid for your liquid test kit?
If you use your test kit on the ph 7 fluid do you get a reading of 7.

If you put your probe back in the 7 solution, does it read 7?
Be sure to dry your probe before it goes in the cali fluid.

[NanoSF]

Good idea redbelly. I will try that when I get home. When I calibrate the numbers are not PH readings so I never know if it is settling on 7 in fact. What I should have done is after calibration stuck the probe back into the 7 PH and seen if it is in fact 7. There might be enough fluid in my test kit calibration fluid to see what it registers.

[HomerJ]

I am not sure if it does, but the RK should adjust ph according to temp. Ph is a function of temp. Does your test kit take this into account?

The RK does adjust to temp.  Test kit does not specify, although I would like to think they have been made to make measurements at the (or around) typical tank temperature.

What if you use your calibration fluid for your liquid test kit?
If you use your test kit on the ph 7 fluid do you get a reading of 7.

The test kit does not go lower than 7.8 IIRC, nor does it go above 8.6 or 8.8.  That makes testing the 7 or 10 ph solutions with the  kit impossible.

If you put your probe back in the 7 solution, does it read 7?
Be sure to dry your probe before it goes in the cali fluid.

When calibrating for the RKE, it asks you for 10 first, then 7.  When I'm done calibrating, 7 reads 7 (which makes sense since I stopped calibration at the current point read).  But if I leave it in the solution, it slowly creeps down below 7.  (Which seems to indicater I didn't leave long enough in the calibration solution, but to me it shouldn't take an hour!

[NanoSF]

What I was thinking Redbelly meant was use the solution in your test kit that says it is 8.2 (or whatever it says) and see what your RK says it is. Or the other thing I could have done if I had more calibration solution was do the calibration, then add the probe back into the tank then put it back into the calibration solution 7 and see if it goes to 7.0 PH. If it goes to 6.8 then I know I am .2 off for example.

[redbelly]

The RK does adjust to temp.  Test kit does not specify, although I would like to think they have been made to make measurements at the (or around) typical tank temperature.

The test kit does not go lower than 7.8 IIRC, nor does it go above 8.6 or 8.8.  That makes testing the 7 or 10 ph solutions with the  kit impossible.

When calibrating for the RKE, it asks you for 10 first, then 7.  When I'm done calibrating, 7 reads 7 (which makes sense since I stopped calibration at the current point read).  But if I leave it in the solution, it slowly creeps down below 7.  (Which seems to indicater I didn't leave long enough in the calibration solution, but to me it shouldn't take an hour!

How far below 7 are we talking here?

If your reading is slowly creeping down there can only be one of 2 issues.
1) the controller
2) the probe
As indicated above, get a null plug and you will be able to determine if its the probe that is the issue or the controller. 99% of the time the issue is the probe.


If you are still having issues with this, go back to where you purchased the controller and speak with them. They should be able to help you with this.
Probes typically only have a 3 month warranty.

What I was thinking Redbelly meant was use the solution in your test kit that says it is 8.2 (or whatever it says) and see what your RK says it is. Or the other thing I could have done if I had more calibration solution was do the calibration, then add the probe back into the tank then put it back into the calibration solution 7 and see if it goes to 7.0 PH. If it goes to 6.8 then I know I am .2 off for example.

Bingo

Lets be honest, most of the measurements we take in our tank are ball park figures. If it consistently is dropping by .2 over the course of a day then I wouldnt worry too much about it.

[NanoSF]

Okay so I did some tests. I put my PH probe in my 8.3 reference solution and got 8.1. Then I put the probe in some RO water and got 6.45. So the readings are not correct but also doesn't seem to be off by a consistent amount. Unless my RO water (from Watermart in Bells Corners) is lower than the standard 7.0, I haven't learned much except it is not working correctly. I figured I was about .2 low, but the RO water was way lower than that. Does anyone think store bought RO is possibly that much lower than 7.0? Meaning, I was expecting a reading of 6.8 to remain consistent. The only other option is that my number is low on a sliding scale. For example at around 8 I'm off by .2, but around 7 .5 off, and then possibly 1.0 off around 6. So the only thing to do is figure out if it is the probe or the unit. I guess I have to figure out how to rig up a null plug. I still don't quite get what that is but I will look into it.

[omarh]

perfectly normal.....CO2 in the air dissolving in the water raising its acidity.

[RossW]

I hacve never used store bought water... but not sure I would trust it.  Unless you know the store is changing their filters and maintaining their unit, I would assume they are not.

[NanoSF]

I would find it hard to believe that a store with one product...water, would be selling a sub par product. I know that sounds naive but it it just doesn't make sense. I mean they have $200,000 worth of equipment for just this purpose. They let you test the water with TDS meters any time you want. I really don't think they are selling poorly filtered water. I am as skeptical as they come when it comes to businesses ripping people off, but this would just be insane. My feeling was that I might as well buy it from them since I don't have a big tank and their water is filtered with a system no home unit could match. I looked at the cost of the refills and compared it to replacing filters and it seemed to come out fairly even.

Anyway, off topic. I think Omarh nailed it. I didn't think of the CO2 absorption. I mean I think of it in an aquarium, but not in my bottle just sitting there. Makes sense obviously. So maybe I am just .2 off after all.

[HomerJ]

So for those curious, here is a picture of what I think Redbelly calls a NULL plug.  I got it from work, it's a terminator for the old coaxial network cables.  It's just a connector with a fixed resistance (in this case 50ohms) between the ring and the tip.

I plugged it in my SL1 instead of the ph probe, and I get stable readings when I simulate calibration.  That at least proves the controller is ok and works as it should.  I'll try a different pH probe and see if it makes a difference.