Help me dial in my SWG -- How much UV does an auto cover block?

[treyrich]

Alright, here's some background, after going through the SLAM process a couple of times before it "took" (clearly I missed something the first time despite passing the OCLT) I think that I've got the pool free of anything actively consuming my FC (evidenced by my passing the OCLT last night with 0 loss).

I'm having the most difficult time dialing in my SWG, it feels like my chorine demand is going up, but I don't see how that's possible if I'm passing the OCLT. The only thing that I can think of is maybe the UV reaching the pool through the auto cover is a lot stronger than I think it should be? If I had to guess I would have said little-to-no UV is reaching the water with the pool covered, however yesterday the cover was only removed before sun was on the pool (for testing) and after sunset (for testing) with no bather load at all for 48 hours. Let me break down those 48 hours:

1. Tested FC and found it to be at 6.5ppm (low end of target)
2. Added 165oz of bleach (adds 5.9ppm FC per poolmath)
3. Increased SWG Percentage (with cover on) to 40% up from 35%
4. Increased SWG Percentage (with cover off) to 70%...This is irrelevant because cover was on for all of this data
5. Waited 24 hours (adds 4.4ppm FC per poolmath)
6. Tested FC and found it to be at 11.5 (with bleach and SWG we should have had a cumulative addition of 10.3ppm FC from bleach + SWG, so if we round that down to 10 that means we had a daily loss of 5ppm which seems on the extreme end even for an uncovered pool, let alone one that was covered 100% of the daylight hours).
7. Waited 14 hours (adds 2.5ppm FC per poolmath)
8. Turned off SWG
9. Waited 2 hours
10. Tested FC and found it to be at 9.5 (which means we had a loss of 4.5 over the preceding 16 hours when factoring in the 2.5 added by the SWG)
11. Waited 8 hours
12. Tested FC and found it to be at 9.5 (which means nothing was lost overnight)
13. Turned on the SWG

So here's where I'm stuck. It feels like my pool is currently burning through ~5ppm of FC per day while covered which feels excessive, but on the other hand I passed an OCLT last night. So should I be turning up my SWG to ~50% when the cover is closed to be making 5.4ppm FC per day? Is it possible that little-to-no UV is being blocked by the safety cover and that this is all UV related loss (even with 70 CYA)? Is something else going on?

This pool is new, just finished in May, I've been adhering to the TFP method as diligently as possible, but between the weirdness that caused my SLAMs previously and the pool being new I've never felt like I truly had my SWG dialed in. I do have the Cover Expansion Card for the Intellicenter which allows me to set different SWG percentages for when the cover is open vs when it is closed. All lights on the SWG are working as expected, and there are small bubbles visible from the returns when the SWG indicates the cell is on, so I don't (as of now) suspect that anything is wrong with the cell...

 

[Rancho Cost-a-Lotta]

I'll be honest with you, I'm not that intelligent. That said, your post is a little difficult for me to follow.

Have tried to determine if your SWG is producing the level of FC increase you expect? How about an overnight chlorine production test? You can do this by running the swg overnight at X hours and 100%. Test before and after that run and compared to the expected effects in Pool Math.

 

[treyrich]

Hahaha. Well I've got to say I'm offended, how do you not understand the ramblings of a lunatic?!

I'm sorry, that post was basically a stream of consciousness.

I'm definitely happy to run an overnight chlorine production test. So you're thinking maybe the SWG isn't producing the correct amount?

 

[Rancho Cost-a-Lotta]

we had a daily loss of 5ppm which seems on the extreme end even for an uncovered pool, let alone one that was covered 100% of the daylight hours

So you're thinking maybe the SWG isn't producing the correct amount?

I agree that 5 ppm is a considerable loss for a covered pool. I'm losing between 3 and 4 ppm under full sun. The production test merely rules out the SWG as a contributing factor.

Double check your CYA level. I recently bumped mine up to 80 ppm. Likely not an issue for your pool while it's covered.

 

[Rancho Cost-a-Lotta]

Have you confirmed the strength of the bleach matches the entry in Pool Math? Have you confirmed through follow up testing the bleach is raising FC as expected?

 

[wireform]

Your pool logs show a 70 CYA 10 days ago which can be easily 60 now so when the cover is open the FC can and will be consumed faster then @80 but I wouldn't just raise it till a final OCLT is performed to be sure there's nothing brewing.

 

[treyrich]

Have you confirmed the strength of the bleach matches the entry in Pool Math? Have you confirmed through follow up testing the bleach is raising FC as expected?

No, I haven't done any follow up testing to determine whether the bleach potentially has lost its potency. But I am certain on the strength (walmart). I'm down to my last 1/2 bottle, and I was going to go pick up a few more this evening. I guess if this is the issue I may not have any way to find out because I missed my window to test. When you add bleach are you typically always doing a follow up test to confirm it's affect?

Your pool logs show a 70 CYA 10 days ago which can be easily 60 now so when the cover is open the FC can and will be consumed faster then @80 but I wouldn't just raise it till a final OCLT is performed to be sure there's nothing brewing.

How often do you think I should be testing CYA? I'm not sure if you're looking at the most recent logs, but I last tested 4 days ago and it was still 70. I'm not sure whether this would make a huge difference with the pool being covered 100% of the time? But I guess it goes back to my question of how much UV gets through a safety cover?

You think that I need to do another OCLT (passed last night with 0 loss)? Or did you mean the Chlorine Production test suggested by Rancho?

 

[wireform]

but I last tested 4 days ago and it was still 70.

Missed that one so then you're good.

 

[Rancho Cost-a-Lotta]

When you add bleach are you typically always doing a follow up test to confirm it's affect?

Not typically. I'm just trying to consider other factors that may affect your discrepancies. The best way to find out your daily loss is to increase FC enough to cover you for the day, then test. Do not increase FC for a period of 24 hours and test again. This completely removes the effectiveness of chlorine and the SWG from the equation.

 

[treyrich]

Ah, good call, ok I can definitely do that. I guess I’ll do the production test tonight just to confirm the SWG functioning, then I’ll dose for the 24 hour loss test starting tomorrow morning. And we’ll go from there.

 

[Newdude]

+1 with Rancho. You'd only test after adding if a question arose, like this. Then you'd add 4ppm (?) and verify you got what you expected.

I bet we rarely get what we thought, but if it's close enough we never know. You'd just think you lost 4 ppm a day instead of 3, when you really only added 3 ppm a day instead of 4.

All I can think of with your struggle is the SWG not reasonably producing, or testing errors. How old is your kit ?

 

[Rocket J Squirrel]

I doubt it's the light, it's the heat. I'm a jug lugger. In the off season, my covered non-SWG pool can get by with 1 gallon of LC per week. In summer, still usually covered, it wants 1 gallon every 2 days. The difference is that the water can get as cold as 45 F in winter and as warm as 88 F in summer.

But PoolMath says 1 gallon is only 2.8 ppm in my pool, so your 5 ppm/day loss is definitely odd.

PS: I've wondered whether the OCLT can be performed during the day with an opaque autocover.

 

[treyrich]

How old is your kit ?

I’d have to check my email from TFTestKits, but maybe 6 months? But I’m also on my second bottle of R-0871 and this one is only like 1 month old (also almost empty with the 3rd standing by)

 

[Newdude]

but maybe 6 months?

Ok so new this season. Sometimes we see ones in service several years later. They all work great until they don't and because it worked fine the last 2 years doesn't guarantee the next two years.

 

[treyrich]

Totally, yeah my pool build was finished in May, so it’s safe to assume everything I have is more or less brand new (including this salt cell we’re now thinking has a potential issue)

 

[treyrich]

Ok...Here comes another stream of consciousness (Sorry Rancho).

So, here's the events from the last several hours:

1. 8:28PM Tested FC at 11
2. 8:30PM Set SWG to 100%
3. 5:30AM Set SWG to 0%
4. 6:15AM Tested FC at 12
5. 6:26AM Added 1g of 10% bleach (pool essentials from walmart, julian date 208 so very fresh)
6. 7:02AM Tested FC at 15.5

Here are my takeaways:

First, I expected the SWG to raise FC by about 4ppm over the 9 hour period (4.1 per pool math), however only seeing a gain of 1ppm is pretty disheartening. It seems to show that there is an issue with the SWG since I clearly passed an OCLT the night before and FC readings were high the whole time after that OCLT, so it seems unlikely that we have organics consuming the FC. The only other explanation that I can come up with is that some how the intellicenter cover card is playing games with the SWG and preventing it from producing at the expected levels, this feels extremely unlikely though because all of the lights on the SWG (flow, cell, salt, percentage) are lit up exactly as expected with the cover on or off, so I have a hard time believing that the cell would be doing something different than it's reporting with the lights.

Second, I expected the gallon of bleach to raise FC by 4.5ppm (per pool math), but it only raised it by 3.5ppm. This could easily be explained by my only allowing ~35 minutes for the bleach to mix into the pool and perhaps it wasn't fully mixed around (I pull my water for testing on the opposite side of the pool from where the return I poured the bleach into is). I also didn't actually measure the bleach I was putting in, I just poured the whole jug in because I was going for a gallon, but there's nothing to say that the volume and potency of the bleach couldn't have been 'off' enough for the 1ppm difference in expectations here. Overall I think that we can write the 1ppm difference off to environmental factors and say it's good enough.

Finally, I have now started the 24-hour chlorine loss test to determine the daily usage of the pool, so I plan to leave the SWG at 0% and see how much chlorine we're using. With that said, I expect it will be extremely small (dependent on bather load for the day) because it now seems clear that the SWG isn't producing much/any chorine so all of my previous numbers/assumptions may be off base.



So now the question becomes, is there additional testing that I can/should do on the cell before I raise this as a warranty issue? Or should I get my builder/pentair involved now?

 

[Newdude]

So now the question becomes, is there additional testing that I can/should do on the cell before I raise this as a warranty issue? Or should I get my builder/pentair involved now?

Sorry you got the results you did, but zeroing in on a problem is always a great thing. Pull the cell and inspect it for scale. If it's not gummed up, and you confirm the automation isn't turning it off after it's running for some hours, then it's a mechanical issue for the PB.

 

[treyrich]

Alright! Yeah, even unfortunate progress is better than no progress. I'll check the cell this evening when I'm back at the house, would shock me if there was scale on it because I've kept all my numbers (except FC) pretty stable within recommended values. I'll report back here once I inspect the cell.

 

[Newdude]

would shock me if there was scale on it because I've kept all my numbers (except FC) pretty stable within recommended values

It's always possible and it would be an easy fix. It's also more ammo if it's clean when the PB has excuses why its not their issue.

 

[Rancho Cost-a-Lotta]

Just got back in from my bike ride to see the bad news. Are your confident on the pool volume? Are you sure you have an IC 60?

The cell and system should be under warranty so don't sweat it for now. Do some checking to see if you need to deal with the installer or Pentair. You might want to contact support for guidance. Maybe @Jimrahbe or @JamesW can stop by and provide some tips for troubleshooting. Take a look at the article below for some guidance.

FYI, liquid chlorine should have a "Julian date" on the jug or box that shows the day of manufacture. It's 5 digits with the first two being the year and last three being the year (ex 23123...123rd day of 2023).

Pentair Intellichlor ICXX SWG - Further Reading

www.troublefreepool.com