SWG Only Putting Out 3ppm Free Chlorine

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packetfire

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Sep 7, 2018
34
Jersey Shore
I have a little Intex SWG, which has been fine for my small above-ground pool in prior years.
It has a panel that can alert on multiple "alarm conditions", but none have been triggered.

In the past week, even running the SWG for the maximum possible 12 hours that the pump runs each night has not brought the morning FC level up to where I'd like it.
CYA is 60, which has been a fine level in prior years.
FC is 3.0 at most, CC is zero (only two adults use the pool, so CC is always 0.5 or zero in a 10ml DPD test).

Sampling the water coming out of the SWG, which is after the sand filter, just before back into the pool, I again get 3.0 FC in a DPD test, the same as the pool as a whole.
One would think that this would have to be higher than 3.0, if the SWG was to have any hope of ever raising the FC level.

The salt level is fine, alkalinity is fine, and pH the only thing I've needed to occasionally tweak with Borax, but has stayed within the acceptable range (7.2 - 7.8)
I took out both cells (copper cell and SWG cell) and both look fine, no build up between plates, nothing shorting plates out.
I soaked them both in vinegar for 12 hours, just to be sure.

But the output seems low to me - I have never needed to add liquid chlorine to this pool, and I would wake up to FC readings of 5-7 with only 10 or 11 hours of SWG operation per night.

The negligible CC readings and low FC readings make me think that the cell is simply "worn out", and not performing as expected in its 3rd season of operation.

Any opinions?
 
Have u tried doing an Overnight Chlorine Loss Test to rule out algae? If you pass then its likely you need to up your cya to protect the fc the cell makes during these dog days of summer. Adjust your fc w/ liquid chlorine accordingly as per the FC/CYA Levels & see if the cell can maintain it. They do age & slowly lose their ability as well. Occasionally supplementing w/ liquid chlorine may be necessary to ensure you don’t get near minimum for your cya. A few years is a good run for one of those units.
 
Added 30 oz of Clorox, per the "pool math" calculation, but the result after a few hours with the pump running was not an FC of "7". It was "5" using a 10ml DPD test.
Over night, with only the pump running for a total of 12 hours, the 5K gallon pool sank to "4", again using a 10ml DPD test, and there was the rare event of a measurable CC - 0.5 in a 10ml DPD test.

So, yes, there is loss of FC at night, and apparently, consumption of free chlorine that is NOT detected with the CC test.
I fail to understand how chlorine is being "consumed" by (apparently algae) that is both invisible to the very critical eye, in a perfectly clear pool, without it being revealed by the CC test. a "0.5" CC test result, the most I've ever seen, does not account for the loss "pool math" seems to indicate that we are experiencing.

Why don't I have any test results that detect and measure the extent of the problem?

I should note that the amount of gas bubbles produced by the titanium electrode is about the same as I've always seen, so I am not certain that the SWG electrode has worn out. No error codes. The cell was used in 2019, 2020, and now 2021, late April to mid-October.
 
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It’s called nascent algae - not visible but still there eating away at fc nonetheless. Elevated cc’s are one indicator of organics in the water but the absence of cc’s doesn’t necessarily mean there’s nothing growing. That’s why there are 3 end of slam criteria 👇
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You have performed the test that detects & measures the extent of the problem- the Overnight Chlorine Loss Test.
It’s SLAM Process time for you. Lower ph to 7.2 before u begin & raise fc to 24 ppm. Test & Maintain that fc level as often as you can (at least several x’s/day)
Be sure to use liquid chlorine/unadulterated bleach (clorox brand is not recommended as it contains “cloromax”) & leave the swg off during slam as it won’t do much good & it will just put extra wear on your cell. Follow the slam article to the letter. Feel free to Ask questions as u go along.
You may want to retest within 30 minutes of one of your additions to be sure your bleach hasn’t lost potency. If it has just adjust your dosages accordingly.
 
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Hey Packet !!
packetfire said:
In the past week, even running the SWG for the maximum possible 12 hours that the pump runs each night has not brought the morning FC level up to where I'd like it.
Click to expand...
Intex sets their max runtime because the average non-swg pool does not need more than 12 hours. You can always run it for a second cycle, or 2 more hours. Or whatever. Too many people get hung up on 12 hours is enough. If it isn’t, run more, regardless of factory settings.
packetfire said:
CYA is 60, which has been a fine level in prior years
Click to expand...
Every of the last several years has broken the average temp record. It’s funny in a way because we haven’t had any monster weeks long heatwaves in those recent years, but the individual days were a degree or two warmer, raising the average even without the massive heat spikes. Your previous 60 CYA simply may not be cutting it anymore. You want to rule out any need to SLAM, or SLAM first if need be. Once you’re sure the water is clear, go to 70. For reference being pretty close to you, I always needed 70.
packetfire said:
fail to understand how chlorine is being "consumed" by (apparently algae) that is both invisible to the very critical eye, in a perfectly clear pool, without it being revealed by the CC test
Click to expand...
Algae grows exponentially. Those last few multiples make the difference between a little FC loss with clear water and full blown pea soup. Your regular testing gives you the early warning signs that something is amiss. Many newbs fail to listen to their pools and learn the hard way that it wasn’t the filter/swg/etc like they thought.

You’re doing great. Listen to your testing.
 
*also worth noting…. This is TEXTBOOK ‘how to avoid a swamp the TFP way’

1) test regularly to see a possible issue
2) rule out algae before it gets the upper hand
3) manually dose daily to make up the difference which will buy us plenty of time to adjust other things like the SWG / CYA / etc.

3a). Pool stays perfect in the meantime.
4) Back to being trouble free.
 
Be aware that a swg will not overcome algae, they are not designed to do so. They are only designed to replenish the 2-4ppm fc loss per day of the average pool.
If you have a 7k gal intex unit the fc it provides will be consumed by algae quite quickly in your sized pool, w/ a 15k gal unit will take a little longer but it still won’t keep up even if run 24/7 during an algae bloom. Liquid chlorine is the answer.
 
So, things were not as bad as they seemed. Added Clorox, per "pool math" in an attempt to simply get from FC-3 up to FC-16, and most of the Clorox from a still-sealed gallon jug got eaten by this invisible, undetected algae.

So...
Added 30 oz Clorox Tuesday Night, and ran the pump and SWG 12 hours.
6:30am Wed: 14.5 FC, 0 CC, 7.8 pH
6:30pm Wed: 7 FC, 0.5 CC, 7.6 pH
No way sun would lose me 7.5 ppm in 12 hours, so added another 32 oz Clorox Wed Night, and ran the SWG and pump 12 hrs (the max that the timers allow)

8:00am Thur: 9 FC, 0 CC, 7.5 pH
Added nothing to see what the daily "sun losses" would be with the pool just sitting there with the solar ("bubble wrap") cover, and no pump or SWG.

5:30pm Thur: 7 FC, 0 CC, 7.5 pH
Losing 2ppm is reasonable due to sun alone with this pool, so added nothing, just let the pump and SWG run 12 hours

6:30am Fri: 9 FC, 0 CC, 7.5 pH
The above is very encouraging, as the overnight increase of 2ppm from SWG alone is reasonable with this tiny pump and SWG, so another overnight test can be run tonight, as "9 FC" is a bit too high for my wife's bikinis.**

...we shall see...

Bypassing the the "timer" for the SWG and using an external timer relay to run the pump and SWG and the SWG's cooling fan longer than 12 hours may be needed to prevent this, but I had been only running the SWG 10 hours per night during July.

(** Big thumbs up for "Splash" brand swimsuit wash here, as the same Taylor DPD test chems show the removal of Chlorine when washed in this stuff. Washing in Dawn dish soap does not remove the Chlorine, and the test is to soak the suit overnight in a sink, and then test the water in which the suit soaked).
 
To eliminate algae you need to go to SLAM Process level fc for your cya which is 24ppm FC/CYA Levels
&
maintain fc level that until u pass all 3 end of slam criteria as listed above.
The Overnight Chlorine Loss Test is performed without the swg running.
Doing it 1/2 way will just allow it to come back (probably sooner than later) - it may seem gone but you will slowly have higher & higher demand until your swg will no longer keep up once again.
 

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