Source
r/pools•
Pool_Guy

Alright pool pros ... help ME out for a change

I'm relatively new to Chemtrol systems and ORP values in particular ... I'm more of a hardware troubleshooter/repair tech and I know enough chemistry to get by. I have maintained 1 or 2 chemtrol systems over the last few years and now 1 of them is stumping me. I can't get the ORP value to budge from 200 or 201 ... even when adding 30L of liquid chlorine. (200,000L pool). I don't have everything in perfect balance as of yet, but I want to eliminate it being a chemistry issue before I call a tech in that specializes in Chemtrols. My chemistry is close but not perfect yet, not enough to have that much of an issue with the ORP readings (I think). I have replaced both sensors. What would cause that ORP value to be SO low. My understanding is that 200 mv is the lowest range they will read. Do I have a hardware issue or am I missing something in my chemistry? Things are not perfect, but they are close, ph 7.2 and ppm FC 5.0 Pool is clear.

Posted Jun 4, 2017, 4:56 PM UTC · edited

211
hoggy46012•

Almost surely a bad sensor, test the sensor by putting it in your comparator tube filled about half with fresh water, add your acid demand reagent, this should cause the otp to go up, add base demand to see it go down.

ORP stands for oxidation reduction potential, or basically the effectiveness of the chlorine in the water. The reason my test works is because letting pH makes the chlorine in the water more effective, raising it makes it less effective.

I have worked on hundreds of chemically controlled pools over the years, let me know if you have more questions.

2
Pool_GuyOP•

Interesting. I'll try that tomorrow. Sensor is brand new, is it possible to be failed out of the box? I have never seen an ORP sensor fail, but I have had issues with pH a few times. I've never seen this pool below 500mv even after just opening it for the Spring. 200 seems a bit fishy, more than less then perfect chemistry. Thanks for your response.

If I were to test a bottle of off the shelf bottled drinking water, what sort of ORP value would I likely see?

1
hoggy46012•

Since the sensor is new, I would look at the connector and make sure the contacts aren't terribly dirty or corroded. If that isn't the case, a new controller may be in order. You can open that one up and look at the internal wiring but I doubt there is anything the to see.

1
Pool_GuyOP•

That was exactly my troubleshooting flow prior to making my post ... And my reaction when looking at the internal boards. Thanks again.

1
Blithely_Insipid•

Most likely a bad input board in the controller if you're getting the same reading across multiple and new probes. I'd first open up the controller and verify all wiring is intact and look for any obvious problems. I've never worked on any of the chemtrols myself but I work on competing automation controllers, so by the time I'm called in we just throw away the Chemtrols and put in our own. But it definitely sounds like a controller problem and not a chemistry issue. As u/hoggy46012 said, you can always add reagents or liquid chlorine to your test cell and see if the reading changes.

2
Pool_GuyOP•

Thanks for this response, I wasn't sure if their could be a problem in the boards or not, I'll perform the reagent test with a few different sensors I have on hand and if they are consistent then I think it's safe to say it's a hardware issue and I can call in the specialists. Appreciate the help.

1
TyneyTymey•

this guide may help

Judging by what you've explained, the ORP sensor you've replaced may have been done wrong (I recall they can't be dried out or they fail) or may not have been calibrated into the system correctly.

I highly recommend calling Chemtrol (Santa Barbara Controls) and ask them for advice - they are very reasonable and can usually help you through small problems over the phone.

1
Pool_GuyOP•

I've tried 3 sensors while troubleshooting, 1 which came straight from the wet shipping/storage capsules , they all read the same 200 or 201 mV ... I was just trying to rule out it being some major chemistry issue i was unaware of before taking it to the next step of troubleshooting the circuit boards. Thanks for the input, I've read through that guide a few times and it never mentions a reading of less than 450 so that's what made me think it was a hardware issue.

2
TyneyTymey•

Definitely sounds like a hardware issue.

Again, call the guys at Santa Barbara Controls and while you're in front of the unit, have them help you trouble shoot it. I would guess it's something fairly simple, like possibly the wrong sensor plug or something needing to be reset in the unit. If you get Jacques - ask for someone else! He's the designer/engineer and he's way too smart to help someone over the phone, if you know what I mean.

1
Pool_GuyOP•

Chemtrol unit is faulty, dead ORP circuit. SBC was excellent to deal with ... sending it back for warranty. Thanks for all the troubleshooting help.

1
Rebootkid•

As with all water quality questions, please post all your test values.

I'm not a pro, either, but I believe that ORP effectiveness drops as total dissolved solids increase.

You should be around 400mV to make sure the pool is clean.

If your TDS is in range, clean the probe. If that doesn't do anything, then give the vendor a call.

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