ORP only goes up with non-chlorinating shock

joboo7777

Bronze Supporter
Aug 8, 2020
243
McKinney, TX
Pool Size
15568
Surface
Plaster
Chlorine
Liquid Chlorine
In my pool orp rises as the pool gets shaded and drops as the sun hits it. Something to do with the chlorine cya interaction to sunlight. The less cya I run the greater the orp swing. It’s a rhythm that repeats every day. I run my pump 24/7. It happens even in the winter here as well. Also if I run my waterfall orp rises a lot. So many things affect it. Today my orp ranged from a high of 665 just before sunrise to 570 just prior to when the sun ducks behind some big trees and shades the pool. My cya is 15 and fc was 5 ppm.
You may have already mentioned this in previous posts, but have you validated your ORP results using a different probe?
 

scottts

Gold Supporter
Nov 13, 2019
202
Gilbert, AZ
You may have already mentioned this in previous posts, but have you validated your ORP results using a different probe?
Not recently. I did have to replace my ORP probe at the start of the season. For me the ORP reading is just a relative indication of change. If the range of it stays constant I know things in the pool are good. If it drops suddenly I know something is wrong. I think if you use an SWG you just cant really control it using ORP.

I would love to do a survey on TFP> Who has a system using SWG and dosing to an ORP setpoint successfully? I've not seen anyone yet, but maybe that's because nobody has ever asked that question.
 

joboo7777

Bronze Supporter
Aug 8, 2020
243
McKinney, TX
Pool Size
15568
Surface
Plaster
Chlorine
Liquid Chlorine
Not recently. I did have to replace my ORP probe at the start of the season. For me the ORP reading is just a relative indication of change. If the range of it stays constant I know things in the pool are good. If it drops suddenly I know something is wrong. I think if you use an SWG you just cant really control it using ORP.

I would love to do a survey on TFP> Who has a system using SWG and dosing to an ORP setpoint successfully? I've not seen anyone yet, but maybe that's because nobody has ever asked that question.
Yup understood. Its definitely not a replacement for FC testing. Pinpoint makes a 400mV calibration solution. You might want to consider purchasing some to see how accurate the probe is. Even though it's not necessary, it may help to explain why it's so low with the understanding that Hydrogen may play a part in this.
 

scottts

Gold Supporter
Nov 13, 2019
202
Gilbert, AZ
Yup understood. Its definitely not a replacement for FC testing. Pinpoint makes a 400mV calibration solution. You might want to consider purchasing some to see how accurate the probe is. Even though it's not necessary, it may help to explain why it's so low with the understanding that Hydrogen may play a part in this.
I'm not really sure my ORP is low? Can you even predict ORP generally for a specific FC, pH, CYA and water temp? This chart shows an example of ORP vs CYA at at specific pH and TA. Its from the manual for some dispense system but I cant remember which one.orp vs CYA.PNG
 

joboo7777

Bronze Supporter
Aug 8, 2020
243
McKinney, TX
Pool Size
15568
Surface
Plaster
Chlorine
Liquid Chlorine
I'm not really sure my ORP is low? Can you even predict ORP generally for a specific FC, pH, CYA and water temp? This chart shows an example of ORP vs CYA at at specific pH and TA. Its from the manual for some dispense system but I cant remember which one.View attachment 360758
Those results seem very low. My ORP results are more in line with the FC/CYA ratio and CDC guidelines of 650mV as "Acceptable".

Foe example:
During the day, My ORP fluctuates between 690mV and 715mV as Chlorine is being dispensed. This keeps me between 2 and 3ppm. Still higher than the minimum of 1.125ppm based on Richard Faulk's ratio. Although I have never let my ORP go down to 650mV, I suspect if it did it would be around 1.125ppm.
 

joboo7777

Bronze Supporter
Aug 8, 2020
243
McKinney, TX
Pool Size
15568
Surface
Plaster
Chlorine
Liquid Chlorine
Maybe its the salt??

Take a look at this post related to reef keeping and ORP. Randy Holmes Farley who studied Biology and Chemistry at Cornell replies to the post. Of course the salt level is much higher in reef keeping, but maybe it also applies to Pool salt and ORP as well.
 

scottts

Gold Supporter
Nov 13, 2019
202
Gilbert, AZ
Those results seem very low. My ORP results are more in line with the FC/CYA ratio and CDC guidelines of 650mV as "Acceptable".

Foe example:
During the day, My ORP fluctuates between 690mV and 715mV as Chlorine is being dispensed. This keeps me between 2 and 3ppm. Still higher than the minimum of 1.125ppm based on Richard Faulk's ratio. Although I have never let my ORP go down to 650mV, I suspect if it did it would be around 1.125ppm.
I think that's the advantage of LC dispensing. you don't get all these "byproducts" that SWG generates.
 
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scottts

Gold Supporter
Nov 13, 2019
202
Gilbert, AZ
Maybe its the salt??

Take a look at this post related to reef keeping and ORP. Randy Holmes Farley who studied Biology and Chemistry at Cornell replies to the post. Of course the salt level is much higher in reef keeping, but maybe it also applies to Pool salt and ORP as well.
Interesting. I haven't tested for iron copper, phosphates or nitrates in a long time. Maybe I'll do that to see what's what. Who knows what trace elements are in a bag of salt. That's why I'd REALLY love to know if there are ANY people successfully dosing SWG to an ORP setpoint. At this point I don't believe so.

If I shut my cell off I can easily get to 700+ ORP after a few hours. But when the cell is generating - no way.
 

joboo7777

Bronze Supporter
Aug 8, 2020
243
McKinney, TX
Pool Size
15568
Surface
Plaster
Chlorine
Liquid Chlorine
Interesting. I haven't tested for iron copper, phosphates or nitrates in a long time. Maybe I'll do that to see what's what. Who knows what trace elements are in a bag of salt. That's why I'd REALLY love to know if there are ANY people successfully dosing SWG to an ORP setpoint. At this point I don't believe so.

If I shut my cell off I can easily get to 700+ ORP after a few hours. But when the cell is generating - no way.
Yea, Unfortunately I don't think you'll find what you're looking for on this forum. It's too bad you don't have an extra salt cell laying around to rule that out as well. ;)
 

Charles Bezzina

Well-known member
Jul 10, 2021
82
Sydney Australia
Pool Size
38000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Hayward Aqua Rite (T-9)
The good people at Hayward have sent me a replacement ORP probe. After 24 hours, it appears the mV output no longer goes down when the pump or chlorinator is running. I'll know more after a week of monitoring.
 

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joboo7777

Bronze Supporter
Aug 8, 2020
243
McKinney, TX
Pool Size
15568
Surface
Plaster
Chlorine
Liquid Chlorine
The good people at Hayward have sent me a replacement ORP probe. After 24 hours, it appears the mV output no longer goes down when the pump or chlorinator is running. I'll know more after a week of monitoring.
Definitely keep us posted. Success with ORP and SWG is hard to come by. I’m sure others on the forums will be interested to learn the results.
 
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Charles Bezzina

Well-known member
Jul 10, 2021
82
Sydney Australia
Pool Size
38000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Hayward Aqua Rite (T-9)
Hi joboo.

The replacement probe is definitely performing better than the original. ORP appears to remain stable while the pump is running and goes up a little while the chlorinator is producing at 25%. (I have not tried to see what happens at 100% production)

What I really notice is that the day to day variation in ORP makes it too difficult to choose a meaningful setpoint, so I'm happy to leave it in percentage mode, and perhaps in the future configure the setpoint as a high limit while still running in percentage mode.

I don't have the ability to log the ORP automatically so I'm only able to go by my observations, but I'd say at this point it seems to be working. One day I'll look at it a bit more closely to try and better utilise it.

I will say anyone who has a Hayward ORP probe that responds backwards, or fluctuates between extreme values should probably test/repair/replace the ORP probe.
 
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