Disable ORP for a better performance outcome?

[learthur]

Strong work. Everyone has given you great advice.

I would add this:

1). Don't adjust your setpoint yet.
2). Wait at least 3 days between adjusting ORP setpoint and then don't move it more than 30 mC either direction.
3). With time your mind will get the hang of the ORP numbers.
4). Keep your ORP probe and pH probes CLEAN.
5). I am not sure if you will need to, but I calibrate my pH probe every 1-2 months.
6) If things get crazy: remove ORP and pH probes and soak overnight in a potassium based electrode storage solution, shock pool, dip the ORP probe in a 1:5 solution of bleach and water for 5 minutes and reinstall everything.
Good luck

Lee

 

[Lazyman]

Good stuff, thanks.

I couldn't wait, I saw FC dropping quickly today, so I changed orp to 650 so it could turn on. It did start producing immediately. this is the first time in several days that the unit is even "ON". I know I shouldn't be changing it so often, but the other times I've changed it, there was no effect. It was still "OFF" as the setpoint was always higher than the actual orp reading. Now that FC was 1.5, I figured I should change it to turn on. That was getting a little low.

Orp reading was 660 and FC test was 1.5, so I changed setpoint to 650 and it's running now. I'll see what it produces at this level.

Yesterday the orp reading was hovering at 650 for a while, so this might be a good number. I just couldn't have the FC go down any lower than 1.5, correct?

8:30 AM = FC-3
12 Noon = FC-1.5 (Now there is chlorine production)

 

[Lazyman]

4). Keep your ORP probe and pH probes CLEAN.
6) If things get crazy: remove ORP and pH probes and soak overnight in a potassium based electrode storage solution, shock pool, dip the ORP probe in a 1:5 solution of bleach and water for 5 minutes and reinstall everything.

Lee

I'm going to clean them possibly tomorrow. Can I get the "potassium based electrode storage solution" at a pool store like Leslies? Anywhere else? I'd rather not wait for online delivery if I don't have to.

The update is not good. It was going, sort of, OK for a while, but is now off again. ORP readings are crazy. Up and down 100+ points with no rhyme or reason. FC went down to 1 the other day and orp reading wasn't even close to turning on. This was after a week or two of working OK.

My pool may be too small for the system. I have a 48 size cell and it produces a lot of chlorine and shuts off for many days. This, in turn, brings the ph down because there is no chlorine being produced. I have to add borax frequently because of the low ph levels. Then it's a roll of the dice if it turns on the chlorine production when the Fc goes down to low levels again. This last time, it did not turn on at FC of 1, so I manually added bleach.

Anyway, I'm going to clean them and check everything again. If this doesn't work, it may be the end of it. Unless I call a technician to come out to the house. Tech support said they would do that. no idea what they would do.

Thanks

 

[JasonLion]

How committed are you to getting the ORP sensor to work? Everything will work more reliably, at least compared to your experience so far, in percentage based mode, with ORP disabled, at least once you figure out an appropriate percentage.

 

[Lazyman]

How committed are you to getting the ORP sensor to work? Everything will work more reliably, at least compared to your experience so far, in percentage based mode, with ORP disabled, at least once you figure out an appropriate percentage.

If it will ultimately work, then I'll do some more tinkering. I'm not sure if it would be worth it. I know I can "give up" and just go the percentage route at anytime. So there's something to fall back on. I just want a little more time with this first. Maybe until September. Wait, in NJ that's all I've got! lol

My wife sees me testing every 2 hours and says "I thought this was an automated system".

Honestly, I AM a lazyman, and I did want it as automated as I can get it. I like to 'set it and forget it' type of thing. So, if you have any ideas for this first, I'll try them. However, I am very close to scrapping it and going with the precentage based solution.

 

[JasonLion]

When the SWG runs, it produces small hydrogen bubbles. You want those bubbles to come out of the water, instead of dissolving. Sometimes, aiming your return jets up towards the surface can help prevent the hydrogen gas from dissolving. Dissolved hydrogen gas will lower the ORP reading, so minimizing the amount of dissolved hydrogen can help.

 

[Lazyman]

When the SWG runs, it produces small hydrogen bubbles. You want those bubbles to come out of the water, instead of dissolving. Sometimes, aiming your return jets up towards the surface can help prevent the hydrogen gas from dissolving. Dissolved hydrogen gas will lower the ORP reading, so minimizing the amount of dissolved hydrogen can help.

Ahhh, I do notice a lot of tiny bubbles around the area of the return. I've even noticed them INSIDE my flow gauge, which is now useless when the swg is running because it lifts the float up higher than normal. When the swg is not running, the gauge works fine.

I don't know if the pressure is high enough to force the bubbles up out of the water. I have 28gpm on low speed. It does feel like a strong flow out of the return, but there are no bubbles of any kind that are visible when pointing the return up. No aeration type bubbles. I will try that however. Thanks. ***EDIT #1** Yes, there are aeration type bubbles with the low speed return jet pointing up. YES! I've switched it to this position and it is now creating that effect. I hope this will take care of the ph issue as well. I just need to keep an eye out for the TA in a different light.

If I have to change it to high speed, I will do that as well. Right now I'm running it 24/7 on low, so I'd rather not switch to high. I was hoping to figure this out first, then start messing with run times for filtering. 330 watts of electricity on low speed, is great. I'll leave it there for now if I could.


**Edit #2

Maybe I should install those home made aeration pipes that go onto the return fitting. I've just seen the thread about it and it seems like a good idea. Will that do the trick with the bubbles?

 

[rowdydoc]

Hi,

I apologise if I have not taken in all that was in this thread - but time is short and I only read the first and last pages...

I have been down the path of trying to automate a SWG with ORP or FC (HOCl) feedback and would like to contribute my thoughts:

1. I have read many times that feedback control of SWG is not of great benefit due to stable usage of chlorine being able to be matched to fixed production level from the SWG. This has not been my experience and I think that is because I am religious with the use of my pool cover. The pool cover blocks UV light and prevents a huge proportion of the breakdown of FC. This means if I don't swim for a few days my SWG builds up the FC much too high - hence the benefit of feedback control. I am not willing to ditch the pool cover as it is of great benefit for both water and energy use reduction.

2. I have found that the link between CYA and ORP is that CYA can prematurely "foul" the ORP probe resulting in a degradation of its readings over a much shorter interval than expected in CYA free water. Other than that I have found that using a hand-held ORP probe (ie not permanently immersed in the CYA water) has provided very consistent correlation between mV and HOCl over 2 years of operation (ie compensating for minor pH swings). Note that this is for a fixed CYA level of 50ppm. If the CYA level changes then the correlation between mV and HOCl changes.

3. All this sound great until you add in the dissolved hydrogen gas from the SWG. I think for me it is extreme because of my fastidiousness with the pool cover. The pool cover being on so much means there is much reduced natural exchange of the dissolved hydrogen gas out of the water into atmosphere. This build-up of hydrogen is the killer for the ORP probe measurement as it is an interference with its measurement to the point of it being useless. I have done many tests now and shown that by vigorously stirring a pool sample the ORP reading can be returned to the expected value for the measured HOCl (via FC test) within 10-20 minutes. There is also a pH increase that occurs in these tests that I put down to release of CO2. The pH change seems to be "real" as I see it on the pH electrode and the pH test kit. I have come up with no way of keeping the hydrogen build-up under control (jets up/jet down/flow rate change/etc) - it just seems to be bad for my pool/SWG.

4. Not to be defeated I found a HOCl probe that was both cost-effective and not affected by CYA (ie good reproducability and lifetime). An added benefit was that it has a replaceable head! Very excited then found that it too is interfered with by the dissolved hydrogen (arghhhh!).

5. Threw in the towel with the SWG and decided to use a peristaltic dosing pump to control FC/HOCl levels automatically. No hydrogen - no problem. A very disappointing result as the SWG is clearly the most convenient approach to pool sanitation - but I guess life is never as simple as we sometimes wish...

I'm an electrical engineer in control system / automation so that part of it doesn't phase me. The chemistry was a bit of a learning curve though :?

So if you want to check if the dissolved hydrogen is doing your system in - I suggest you take a water sample and put the ORP probe into it and then stir or shake away!

 

[learthur]

I can also confirm what rowdydoc posts above.

I had great success using ORP when I used bleach before installing the SWG. After installing the swg ORP values became depressed due to an interfering substance generated by the swg. It may be hydrogen, I don't know. I do know that. As rowdydoc described above taking a water sample in a glass and letting it sit 20 minutes or so did restore reliable ORP measurement.

As a side note before installing the SWG I tested ORP vs CYA at various concentrations from 20 - 100 ppm and it made little difference in practical use I.e. The relationship between ORP and HOCL was still there. So no, I don't believe CYA is the problem. Hydrogen maybe.....

From a practical standpoint the swg is great for my outdoor pool. I adjust it up or down about 5% once a week and FC levels are very stable. Very happy with my trouble free pool.

Lee

 

[Lazyman]

**Update. Pointing the return up, out of the water, made a big difference in readings. TA and CYA at low(er) levels seem to work better with my system. The system was working fine towards the end of the season. I was pretty happy with it's operation at that point.

Thanks to everyone for their help.

Next year will be my first "opening" after the winter. I need to clean the sensors by then. I hope they're fine sitting in the salt solution until I clean them. I didn't think of having spare (pool)water to soak them in after I cleaned them over the winter. Not sure where I'll store them now. The pool is a block of ice, so I can't get a small amount of water now.


PS I use my "trouble free" coffee mugs religously. I love them! lol

 

[chem geek]

Not sure how the orp sensor can know the difference. CYA is CYA.

ORP is roughly measuring the oxidation-reduction potential of the water and the strongest oxidizer in the water by far is hypochlorous acid. This is NOT the same thing as the Free Chlorine (FC) level because when Cyanuric Acid (CYA) is present, most of the chlorine binds to it and is not an oxidizer of any reasonable strength. So, in effect, the ORP sensor is roughly reading the hypochlorous acid concentration, though it is also pH dependent in a way beyond that of this concentration.

Different ORP sensors from different manufacturers often get different readings even on the same water. You can't really rely on them as an "absolute" measurement in spite of what these manufacturers may tell you.

As an example, the following are ORP readings from two different sensors (based on models of measurements from manufacturer tables and/or field measurements) at different chlorine and CYA levels (these are at a pH of 7.5).

FC .... CYA ..... Chemtrol .... Oakton
1 ........ 0 ........... 762 ........... 739
1 ........ 5 ........... 704 ........... 667
1 ...... 10 ........... 681 ........... 637
1 ...... 20 ........... 658 ........... 608
4 ...... 20 ........... 710 ........... 674
4 ...... 40 ........... 683 ........... 640

Basically, you should just use the ORP as a process control device for maintaining an FC level that you have designated as appropriate for your CYA level. Not having any CYA at all has the chlorine be very strong.