Chlorine generation (SWG) and flow: increased flow for a day and my FC shot up

[dandannoodles]

I run my VSP 12 hours a day, at 1800rpm, from 8am to 8pm. I just fired it up on July 5th, the day after all my salt, so I've been tracking my levels pretty carefully since then. It's been holding pretty steady for several days and went up yesterday, and I'm trying to figure out why.

Here is my FC readings for the last several days:

• 7/5 - 6.0 (had added liquid chlorine to get it to this level before starting the SWG)
• 7/6 - 4.5
• 7/7 - 4.5
• 7/8 - 4.5
• 7/9 - 7.0

My kids wanted the bubblers on higher so I ran the VSP at a higher setting, something like 2800rpm for most of the day and when I checked my chlorine at 7pm last night, I was a little surprised to see it at 7.0.

Rest of my levels:

• CC: 0
• pH: 8.0 (I'm trying to get my pH and TA balanced... it's been around 7.9 to 8 most days)
• TA: 90
• CH: 375
• CYA: 70
• Salt: 3800
• Water temp: 80F

Any thoughts? Thanks!

 

[BDY]

SWG FC generation is a function of run time or % setting… not flow volume. As I understand it low salinity can also make it struggle to generate on some SWG as well

Could you have run the pump longer than normal that day?
Was it more cloudy that day so less UV degradation? FC usage varies by weather.
Less swimming load that day?
Tested the FC at different times of day? I know for my testing it can vary a lot depending on time of day

maybe others have other thoughts…

 

[Zalligan]

Was it more cloudy that day so less UV degradation? FC usage varies by weather.
Tested the FC at different times of day? I know for my testing it can vary a lot depending on time of day

First two that came to mind for me as well. Cloudy, lower UV days have caused my chlorine to jump a bit from time to time, but I could definitely see the timing be bigger culprit. Testing at 7pm, sounds like OP tested at the end of the chlorine generation period, and if used to testing in the AM, after no production, could definitely see those readings being lower.

OP - any rhyme or reason to your pump schedule? I personally run my VSP 24x7 at the lowest speed I can run it (+~50rpm) that will trip the flow switch. For me, this is around 1350rpm. Definitely helps with consistency/predictability of my testing. Also, using my pump as a rough estimate (YMMV), running 24 hours at 1350 burns about the same amount of electricity as I would at 1800rpm for 12 hours (1350 may be a touch more efficient).

 

[JJ_Tex]

Have you confirmed that the SWCG flow light stays green at the lower speeds? I try to run mine as low as possible, but will have to increase the RPMs since the flow light will come on as the filter gets dirtier.

If yours does the same, maybe your pool is not producing chlorine for the full time the pump is running.

 

[Zalligan]

but will have to increase the RPMs since the flow light will come on as the filter gets dirtier.

This is how I know it's time for a filter cleaning

 

[dandannoodles]

SWG FC generation is a function of run time or % setting… not flow volume. As I understand it low salinity can also make it struggle to generate on some SWG as well

Could you have run the pump longer than normal that day?
Was it more cloudy that day so less UV degradation? FC usage varies by weather.
Less swimming load that day?
Tested the FC at different times of day? I know for my testing it can vary a lot depending on time of day

maybe others have other thoughts…

Nope, bright sun. Normal schedule just higher flow.

Anyways I just checked it and it's at 9.5 so I'm going to turn the SWG down to 30% and see if that brings my FC down.

 

[dandannoodles]

First two that came to mind for me as well. Cloudy, lower UV days have caused my chlorine to jump a bit from time to time, but I could definitely see the timing be bigger culprit. Testing at 7pm, sounds like OP tested at the end of the chlorine generation period, and if used to testing in the AM, after no production, could definitely see those readings being lower.

OP - any rhyme or reason to your pump schedule? I personally run my VSP 24x7 at the lowest speed I can run it (+~50rpm) that will trip the flow switch. For me, this is around 1350rpm. Definitely helps with consistency/predictability of my testing. Also, using my pump as a rough estimate (YMMV), running 24 hours at 1350 burns about the same amount of electricity as I would at 1800rpm for 12 hours (1350 may be a touch more efficient).

Nope, no real reason other than it felt right to me... Haha. I am sure I could turn it down and increase the duration. Is there a reason why you run yours 24/7 at a lower RPM? I would guess if I did that I would need to turn the production on my SWG way down. Seems like at 50% 12 hours a day I am producing too much chlorine.

 

[BDY]

Use pool math app, effects of adding, and select SWG. Enter your salt cells rated production in pounds, your pool size, pump run time, and cell setting and the app calculates the daily FC generated. It’s a good tool to get sn idea of how much FC you are actually generating.

Also you can do a daily chlorine loss test. Turn off the salt cell, Raise the chlorine to a higher level at night. Test 30 minutes after running pump. (Say it results in Fc 10). Leave cell off and measure again same time next evening. (Say now 6). Then it approximates your current daily Fc usage (ex 4). YMMV with weather and bather load, but again it would give an approximate baseline to align the production with (i like to set s little higher daily net add just to be safe and then every once in a while turn the cell off one day if it gets into the Mid teens)

Just some thoughts

 

[BDY]

Ps - The IC 40 is rated at 1.4
Enter that in the production field

 

[Zalligan]

Nope, no real reason other than it felt right to me... Haha. I am sure I could turn it down and increase the duration. Is there a reason why you run yours 24/7 at a lower RPM? I would guess if I did that I would need to turn the production on my SWG way down. Seems like at 50% 12 hours a day I am producing too much chlorine.

Looks like @BDY has you covered on the chlorine piece.

I run 24/7 for better predictability in my testing, and lower energy usage with equivalent turnover. I’ve also read that start/Stop cycles are harder on the pump motors than continuous running, so that may be an added benefit.

 

[Bperry]

I run my VSP 12 hours a day, at 1800rpm, from 8am to 8pm. I just fired it up on July 5th, the day after all my salt, so I've been tracking my levels pretty carefully since then. It's been holding pretty steady for several days and went up yesterday, and I'm trying to figure out why.

Here is my FC readings for the last several days:

• 7/5 - 6.0 (had added liquid chlorine to get it to this level before starting the SWG)
• 7/6 - 4.5
• 7/7 - 4.5
• 7/8 - 4.5
• 7/9 - 7.0

My kids wanted the bubblers on higher so I ran the VSP at a higher setting, something like 2800rpm for most of the day and when I checked my chlorine at 7pm last night, I was a little surprised to see it at 7.0.

Rest of my levels:

• CC: 0
• pH: 8.0 (I'm trying to get my pH and TA balanced... it's been around 7.9 to 8 most days)
• TA: 90
• CH: 375
• CYA: 70
• Salt: 3800
• Water temp: 80F

Any thoughts? Thanks!

If you had low chlorine for some time before turning it on, there may have been algae starting to reproduce and consuming extra chlorine for the first few days. If it died off, you started losing less chlorine. Only other possibility I could come up with.

 

[dandannoodles]

I lowered the SWG to 30% two days ago to see if my FC would come down. I checked yesterday and FC was 10.5! Compared to 9.5 two days ago. So it's still going up even though it's very warm with full sun lately here in Socal. So I dropped the SWG down to 20% and reduced pump time by an hour.

 

[Bperry]

I lowered the SWG to 30% two days ago to see if my FC would come down. I checked yesterday and FC was 10.5! Compared to 9.5 two days ago. So it's still going up even though it's very warm with full sun lately here in Socal. So I dropped the SWG down to 20% and reduced pump time by an hour.

That’s just the way you need to do it.

 

[Zalligan]

Agreed. I leave pump time alone but test/adjust swcg output every 2-3 days just to stay on top of things. As was mentioned, i use the pool math app to get an idea of where it needs to be set. For instance if i went from 9.5-10.5 over 2 days, I'd reduce my swcg output by the corresponding percentage that would reduce daily output by .5ppm and then check again in a few days. It's rare I check my chlorine and DON'T make minor adjustments to swcg output.