What is consuming chlorine?!? SWCG can't keep up. Been SLAMing. Crystal clear pool now. Never algae on walls .

[TaylorN]

It takes 12 hrs of pool pump running at 25gpm (1800rpm) with SWCG running at 100% to maintain chlorine level on covered pool!!! that doesn't sound right?

In past summers (owned house since 2018 and all new equipment was installed) I might get up to 95% swcg with 8hrs of pump run time.

Around mid July there was one day where I was wearing goggles in pool and it seemed like the water was reflecting greenish and just ever so slightly cloudy (if I were to reach), but didn't think anything of it. It almost seemed like an optical illusion, but maybe the start of green algae (?). There has never been anything growing on the walls like slime, dirt, brown, green, etc. But the next time I got in the pool a couple weeks later that greenish look wasn't there and it was crystal clear.

The pool started dropping to 0fC without being able to catch up so decided to look into SLAMing. The COVERED pool has been at CYA 35 and now the free chlorine has been around 14-18fC for just shy of a month. It is currently stable, but I would have figured the chlorine level should be sky rocketing, not maintaining day over day.

Check signature for pool/equipment details. Pool is covered all day (no light). No water auto-fill. Manual fill only. And since it is covered I might only add one inch of water every month or two during summer. Definitely no major leaks.

And I have a pool service guy that comes weekly. He maintain salt, CYA, pH, and adjust SWCG % as needed (pool pump schedule stays the same). Standard stuff. His main purpose is to keep an eye on our pool when I forget to monitor. I do take my own measurements every few weeks.

Normal peak summer Pump schedule (SWCG 95%)
----------------------------------
8am to 5pm at 1800rpm (25gpm), with 1.75 hrs of 2850 rpm (55gpm) runtime throughout that window of time.

Events ( by the way I test the pool at about 10am each morning which is 2 hours after the pump starts):
----------------------------------
7/26 pool was maintaining around 3-4fC with pump running 8hrs a day running 95% SWCG, and pool service sent me text the pH was at 7.4 and hasn't risen in a month which he found odd.
8/6 big pool party. water temp was 87F. HAVEN'T USED POOL since this date. It has been covered all day except for servicing even until today.
8/8 pool was 0fC so I watched service guy dump 1 gallon of 12.5% chlorine in pool, which brought it up to ~3.4fC later in the day
8/15 pool is 0.2fC
8/17 I tested CYA, it was below 30 (past last line on test kit). Added 2.5 gallons of 10% chlorine. Pool now 12-15fC after 4 hours of mixing at "high" speed (2850rpm/55gpm)
8/18 pool 7fC, so it dropped about half overnight. Pump is now running for 12 hrs each day at 100% SWCG at 2850rpm/55gpm. Tested for chloramines and there were none.
8/19 Pool 5.5fC
8/21 Pool 5.5fC
8/22 service guy confirmed CYA is 25. He added 2.5lbs of CYA, which made the pool rise to 35 CYA. Dumped a bunch of liquid chlorine in pool. brought it up to 16fC
8/23 pool 14fC
8/24 pool 13.5fC Decreased pump run speed back to 1800rpm/25gpm (still runs at 2850rpm/55gpm 1.75hr/day)
8/25 pool 14fC. Decided to increase runtime. pump running 12am to 5pm (17hours) at 100% SWCG
8/26 pool 15fC
8/27 pool 16fC
8/28 pool 17.5fC. Reverted schedule back to 12hrs per day at 100%
8/31 started manually running pool water through solar panels at night time from 8pm to 8am (as not to actually warm up the water/
9/5 pool 18fC
9/13 pool 18fC. Pool is still running at 100% SWCH for 12 hours. why would it take that much running to maintain the same level of chlorine especially when the pool is at SLAM levels?

Current stats:
----------------------------------
Free Chlorine 18fC. (I only tested for chloramines starting 8/18, and have not had any since then)
pH: 7.4. It takes 3-4 weeks to rise to 7.6, which is strange because its usually like clockwork rising from 7.4 to 7.6/7.7 each week (before this summer)
CYA: 35 ( matches service guy's reading). Pool guy said he brought CYA up to 60CYA with 6lbs on 4/11/2023. All I can do is believe him. I didn't verify until the chlorine problem started occurring. Either something consumed the CYA or it was never brought up. But I talk to the service guy a lot and believe he actually did it considering how weird the pool is now.
Ammonia: (which I read can deplete CYA?) with new strips, and it was a 0.
total alkalinity: 105-110
Calcium Hardness pool=500. Tap water=240
Salt:3600 (taylor kit)
Pool temp:78;
TDS Measurement: 5300 - Salt 3600= 1700ppm

Other notes:
----------------------------------
I replaced SWCG in April 2022 after it started giving errors. Borrowed a brand new SWCG 3 weeks ago to try to prove SWCG is not the problem. Tt produced the exact same level of free Chlorine in the return line to the pool. At 25gpm the difference between the pool fC and the return fC was about 1.8ppm, which seems right? With my SWCG, every time I look at the pool, champagne bubbles are coming out of the returned. If I set the SWCG to 0%, the bubbles stop. I set the SWCG % to 100% and the bubbles start. I am pretty confident the SWCG is working as expected.

Original cartridge filters ( I cleaned them at the start of summer using this process How to Clean a Pool Cartridge Filter System ) They had a fine layer of brown clay-like slime on them. Got most of that out.


Moving forward
---------------------------------
Pool service guy has no more ideas what could be going. He originally thought it was because the pump was running at too low of speed, but I tried to run the pump at 2850rpm/55gpm for a week straight and that did nothing. He has no idea why/how CYA dropped from 60 to 25 from 4/11 to 8/17 unless he completely blew it. But that shouldn't really matter since its a 100% covered pool, so the chlorine shouldn't be burning up because of the sun. He hasn't tested for Phosphates recently but did a phosphate removal program in spring (multiple weeks), even though there wasn't much phosphates then anyways. and I haven't tested for Copper or Iron.

Today I am going to set the SWCG to 0% with pump running 12hours per day and see how many days it takes to get down to 5-6fC.

For the future, I guess I will just run the pump at 100% SWCG for 12 hours a day at 5-6ppm+ fC for the rest of September until the weather cools down.

Any thoughts? Did I leave out any pertinent details? Should I be doing something differently?











So during the middle of summer the service company said

 

[PoolStored]

Your cell creates 3.2 FC in 12 hours and 100%. When you increased run time, your FC is rising, so you know you are generating.

The likely culprit is your CYA is 35 now, not 60 as is usual. You are seeing higher demand because of lower CYA.

CYA degrades about 5-10 per month, so you should monitor regularly and add when needed. It degrades faster when your pool temps are higher (90s).

Pump speed will not vary the output of the cell, unless your pump speed is slow enough to trigger a no-flow situation with the cell.

 

[Bperry]

It takes 12 hrs of pool pump running at 25gpm (1800rpm) with SWCG running at 100% to maintain chlorine level on covered pool!!! that doesn't sound right?

In past summers (owned house since 2018 and all new equipment was installed) I might get up to 95% swcg with 8hrs of pump run time.

Around mid July there was one day where I was wearing goggles in pool and it seemed like the water was reflecting greenish and just ever so slightly cloudy (if I were to reach), but didn't think anything of it. It almost seemed like an optical illusion, but maybe the start of green algae (?). There has never been anything growing on the walls like slime, dirt, brown, green, etc. But the next time I got in the pool a couple weeks later that greenish look wasn't there and it was crystal clear.

The pool started dropping to 0fC without being able to catch up so decided to look into SLAMing. The COVERED pool has been at CYA 35 and now the free chlorine has been around 14-18fC for just shy of a month. It is currently stable, but I would have figured the chlorine level should be sky rocketing, not maintaining day over day.

Check signature for pool/equipment details. Pool is covered all day (no light). No water auto-fill. Manual fill only. And since it is covered I might only add one inch of water every month or two during summer. Definitely no major leaks.

And I have a pool service guy that comes weekly. He maintain salt, CYA, pH, and adjust SWCG % as needed (pool pump schedule stays the same). Standard stuff. His main purpose is to keep an eye on our pool when I forget to monitor. I do take my own measurements every few weeks.

Normal peak summer Pump schedule (SWCG 95%)
----------------------------------
8am to 5pm at 1800rpm (25gpm), with 1.75 hrs of 2850 rpm (55gpm) runtime throughout that window of time.

Events ( by the way I test the pool at about 10am each morning which is 2 hours after the pump starts):
----------------------------------
7/26 pool was maintaining around 3-4fC with pump running 8hrs a day running 95% SWCG, and pool service sent me text the pH was at 7.4 and hasn't risen in a month which he found odd.
8/6 big pool party. water temp was 87F. HAVEN'T USED POOL since this date. It has been covered all day except for servicing even until today.
8/8 pool was 0fC so I watched service guy dump 1 gallon of 12.5% chlorine in pool, which brought it up to ~3.4fC later in the day
8/15 pool is 0.2fC
8/17 I tested CYA, it was below 30 (past last line on test kit). Added 2.5 gallons of 10% chlorine. Pool now 12-15fC after 4 hours of mixing at "high" speed (2850rpm/55gpm)
8/18 pool 7fC, so it dropped about half overnight. Pump is now running for 12 hrs each day at 100% SWCG at 2850rpm/55gpm. Tested for chloramines and there were none.
8/19 Pool 5.5fC
8/21 Pool 5.5fC
8/22 service guy confirmed CYA is 25. He added 2.5lbs of CYA, which made the pool rise to 35 CYA. Dumped a bunch of liquid chlorine in pool. brought it up to 16fC
8/23 pool 14fC
8/24 pool 13.5fC Decreased pump run speed back to 1800rpm/25gpm (still runs at 2850rpm/55gpm 1.75hr/day)
8/25 pool 14fC. Decided to increase runtime. pump running 12am to 5pm (17hours) at 100% SWCG
8/26 pool 15fC
8/27 pool 16fC
8/28 pool 17.5fC. Reverted schedule back to 12hrs per day at 100%
8/31 started manually running pool water through solar panels at night time from 8pm to 8am (as not to actually warm up the water/
9/5 pool 18fC
9/13 pool 18fC. Pool is still running at 100% SWCH for 12 hours. why would it take that much running to maintain the same level of chlorine especially when the pool is at SLAM levels?

Current stats:
----------------------------------
Free Chlorine 18fC. (I only tested for chloramines starting 8/18, and have not had any since then)
pH: 7.4. It takes 3-4 weeks to rise to 7.6, which is strange because its usually like clockwork rising from 7.4 to 7.6/7.7 each week (before this summer)
CYA: 35 ( matches service guy's reading). Pool guy said he brought CYA up to 60CYA with 6lbs on 4/11/2023. All I can do is believe him. I didn't verify until the chlorine problem started occurring. Either something consumed the CYA or it was never brought up. But I talk to the service guy a lot and believe he actually did it considering how weird the pool is now.
Ammonia: (which I read can deplete CYA?) with new strips, and it was a 0.
total alkalinity: 105-110
Calcium Hardness pool=500. Tap water=240
Salt:3600 (taylor kit)
Pool temp:78;
TDS Measurement: 5300 - Salt 3600= 1700ppm

Other notes:
----------------------------------
I replaced SWCG in April 2022 after it started giving errors. Borrowed a brand new SWCG 3 weeks ago to try to prove SWCG is not the problem. Tt produced the exact same level of free Chlorine in the return line to the pool. At 25gpm the difference between the pool fC and the return fC was about 1.8ppm, which seems right? With my SWCG, every time I look at the pool, champagne bubbles are coming out of the returned. If I set the SWCG to 0%, the bubbles stop. I set the SWCG % to 100% and the bubbles start. I am pretty confident the SWCG is working as expected.

Original cartridge filters ( I cleaned them at the start of summer using this process How to Clean a Pool Cartridge Filter System ) They had a fine layer of brown clay-like slime on them. Got most of that out.


Moving forward
---------------------------------
Pool service guy has no more ideas what could be going. He originally thought it was because the pump was running at too low of speed, but I tried to run the pump at 2850rpm/55gpm for a week straight and that did nothing. He has no idea why/how CYA dropped from 60 to 25 from 4/11 to 8/17 unless he completely blew it. But that shouldn't really matter since its a 100% covered pool, so the chlorine shouldn't be burning up because of the sun. He hasn't tested for Phosphates recently but did a phosphate removal program in spring (multiple weeks), even though there wasn't much phosphates then anyways. and I haven't tested for Copper or Iron.

Today I am going to set the SWCG to 0% with pump running 12hours per day and see how many days it takes to get down to 5-6fC.

For the future, I guess I will just run the pump at 100% SWCG for 12 hours a day at 5-6ppm+ fC for the rest of September until the weather cools down.

Any thoughts? Did I leave out any pertinent details? Should I be doing something differently?











So during the middle of summer the service company said

If you start logging your test results in pool math, we could see the data over time and maybe gives some clues. Is your pool guy using your Taylor kit or something else?

 

[Rancho Cost-a-Lotta]

It looks like your FC dropped to 0.0 a couple days after your pool party. A week later, even after adding chlorine, FC was back down to 0.2. This is a strong indication you probably have algae. You should do an Overnight Chlorine Loss Test.

 

[TaylorN]

Your cell creates 3.2 FC in 12 hours and 100%. When you increased run time, your FC is rising, so you know you are generating.

The likely culprit is your CYA is 35 now, not 60 as is usual. You are seeing higher demand because of lower CYA.

CYA degrades about 5-10 per month, so you should monitor regularly and add when needed. It degrades faster when your pool temps are higher (90s).

Pump speed will not vary the output of the cell, unless your pump speed is slow enough to trigger a no-flow situation with the cell.

I read on Troublefree pools (will need to look it up) that a CYA of 35 is actually recommended for a covered pool since there is no Chlorine depletion from Sun. And lower CYA should make the Chlorine more effective, not that opposite. Its a great opportunity to keep it low since it is already low. We used to always have it between 60-80ppm. And yeah, I will definitely be measuring CYA more often.

Raising CYA will make the chlorine less effective, so if there is by some miracle still some algae trying to fight its way back from oblivion, higher CYA would give it more of a chance to fight back?

 

[TaylorN]

If you start logging your test results in pool math, we could see the data over time and maybe gives some clues. Is your pool guy using your Taylor kit or something else?

I have been taking notes by hand and just added the highlights in this post. I probably should just add test results to pool math instead of notes. That's a good point. Thanks!

Pool guy uses taylor kit, and I do as well (FAS-DPD). I even bought a refill to make sure reagents were fresh. And I am using a syringe to take water samples to make sure the amount of water is exactly what is needed. And I use two scoops of the powder and scrape any heaping amounts so that all measurements are as consistent as possible.

Mainly, Im just trying to find out if:
1) I am crazy and the runtime/swcg% is within reason, or that seems totally crazy and there is obviously something in the water (maybe partial/full drain and refill)?
2) shouldn't a body of water with a consistent 14-18fC and a CYA of 35 or lower, simply nuke any algae or mysterious compound causing chlorine consumption

 

[Bperry]

Mainly, Im just trying to find out if:
1) I am crazy and the runtime/swcg% is within reason, or that seems totally crazy and there is obviously something in the water (maybe partial/full drain and refill)?

If you have algae then it’s within reason that it’s barely keeping up. But no reason to drain and refill without actual reason for doing so.

2) shouldn't a body of water with a consistent 14-18fC and a CYA of 35 or lower, simply nuke any algae or mysterious compound causing chlorine consumption

Not necessarily. Can you format the test results in a way that’s easier to follow? Just the date and the numbers. If you needed to SLAM earlier and didn’t do it then the chlorine consumption could just be “keeping up” from making it go full swamp.

 

[Newdude]

Raising CYA will make the chlorine less effective

Chlorine is chlorine. A little more burns off at higher levels, but the lower level parts of it are equally effective at sanitizing. The higher CYA mostly buffers the higher FC loss, for a wash.

Also, you need to burn off CCs during slam with above normal levels of oxidizing going on. Leave the cover open for the process.

Have you brushed daily ? Checked and cleaned all the hiding in plain sight areas like ladders and light niches ? You may have cleared the water but have residuals lurking, constantly reintroducing the algae.

 

[TaylorN]

It looks like your FC dropped to 0.0 a couple days after your pool party. A week later, even after adding chlorine, FC was back down to 0.2. This is a strong indication you probably have algae. You should do an Overnight Chlorine Loss Test.

Yeah, that is what I was thinking, but figured the Algae should be gone after keeping SLAM level chlorine for almost a month, right? Especially since there was never any actual algae growing on the walls/etc (some crazy quantity). From what I have read, there is always going to be airborne algae that enters pools, and the chlorine will neutralize it. So if we fought off the initial wave of algae, wouldn't the chlorine demand eventually reduce at current SLAM levels?

I have done a handful of overnight chlorine loss tests (per that url), and there is still an over 1ppm loss from 8pm (dark) to 8am.

What blows my mind with all of this is we have a covered pool. Underneath the cover is basically pitch black (I swam under it when the cover came out of its track).

 

[TaylorN]

Maybe its time for new filters? Maybe they contain Crud that can no longer be cleaned out and are just a breeding ground for algae or bacteria (soil)?

Attached are some cartridge filter photos before and after deep cleaning (per link in my initial post). The pool guys said he has never seen that clay like substance on filters, and it never game off with high speed hose spraying.

Previously the pool service guy would just taken them out every 6 months and spend 30-60mins spraying them with a highly focused nozzle. That is why the last one was a super deep cleaning with Acid and TSP on 5/23/2023.

Last week I did open the filter and the cartridges still look like they did post deep cleaning.

They are five years old, so maybe its time to start fresh?

But again, with SLAM level chlorine flowing through them for a month I would think they wouldn't have any "living"/oxidize-able things still stuck in them?

Gosh I am lost

 

[TaylorN]

Chlorine is chlorine. A little more burns off at higher levels, but the lower level parts of it are equally effective at sanitizing. The higher CYA mostly buffers the higher FC loss, for a wash.

Also, you need to burn off CCs during slam with above normal levels of oxidizing going on. Leave the cover open for the process.

Have you brushed daily ? Checked and cleaned all the hiding in plain sight areas like ladders and light niches ? You may have cleared the water but have residuals lurking, constantly reintroducing the algae.

There are no measurable CCs and there haven't been since starting testing for those on 8/18. And the burned off CCs gases would eventually be released since I am opening the cover twice a day, right? or is that not how it works?

And if I leave the cover open for the process, wouldn't I want to raise the CYA? or should I just expect to have to add CYA at the end of the SLAM process?

I did not scrub any surfaces (I could be considered an idiot for intentionally not following those specific directions), because you couldn't see any dirt/grime/algae on any surface at any point. Guess I can start doing that.

As far as reintroducing algae, isn't there always algae being reintroduced on non-covered (aka open aired) pools?

 

[TaylorN]

Pool cover photo

 

[TaylorN]

If you have algae then it’s within reason that it’s barely keeping up. But no reason to drain and refill without actual reason for doing so.


Not necessarily. Can you format the test results in a way that’s easier to follow? Just the date and the numbers. If you needed to SLAM earlier and didn’t do it then the chlorine consumption could just be “keeping up” from making it go full swamp.

Thanks for the quick responses!

here is a more readable format (bear in mind I was taking measurements morning and night for 2 weeks, but these are just the morning measurements):
7/26: 4
8/06: big party. water temp was 87F.
8/08: 0
8/15: 0.2
8/17: 12-15
8/18: 7
8/19: 5.5
8/21: 5.5
8/22: 16
8/23: 14
8/24: 13.5
8/25: 14
8/26: 15
8/27: 16
8/28: 17.5
9/05: 18
9/13: 18

Any big jump was from adding liquid chlorine. Any small jump was adding an extra 5 hours to the already 12 hour run time.

I will take a reading tonight and then again first thing in the morning for another OCLT.

Would it be better to do the OCLT after getting the chlorine level back down to the 5-8 range so I can use a 25ml water sample instead of 10ml sample?

 

[Newdude]

And the burned off CCs gases would eventually be released since I am opening the cover twice a day, right? or is that not how it works?

Nope. That's how it works. I must have missed the open it twice a day part.

Still. I'd leave mine open if it was me. It adds an unnecessary variable.

And if I leave the cover open for the process, wouldn't I want to raise the CYA? or should I just expect to have to add CYA at the end of the SLAM process?

With the SWG off, or on but also adding LC, a 40 CYA (round up) is fine.

If you raise your CYA before its over, the SLAM target raises to match it.

That's the last step

I did not scrub any surfaces (I could be considered an idiot for intentionally not following those specific directions), because you couldn't see any dirt/grime/algae on any surface at any point. Guess I can start doing that.

Thoroughly bush daily at least once. Algae grows a biofolm to protect it from harsh environments. Each pass of the brush exposes another layer to be killed and it could be many thick.

Ongoing slams generally point to the hiding in plain sight algae. You need your AHA moment. Every inch is suspect until it's been cleaned / scubbed. Even the foam on the back of the weir door. Any crevices such as stair trim, auto fills, water features, every last inch.

As far as reintroducing algae, isn't there always algae being reintroduced on non-covered (aka open aired) pools?

There are always organics being introduced but not to the level of crashing a balanced pool. That's where your buffer comes in on top of the daily UV loss, on top of minimum.
#teamrunhot.

 

[Bperry]

I’d X2 the leaving the cover off part. It seems like a lot of these “my SLAM never ends” posts always have the cover as a common theme and removing the cover many times solves the problem.

 

[TaylorN]

Nope. That's how it works. I must have missed the open it twice a day part.

Still. I'd leave mine open if it was me. It adds an unnecessary variable.

With the SWG off, or on but also adding LC, a 40 CYA (round up) is fine.

If you raise your CYA before its over, the SLAM target raises to match it.

That's the last step

Thoroughly bush daily at least once. Algae grows a biofolm to protect it from harsh environments. Each pass of the brush exposes another layer to be killed and it could be many thick.

Ongoing slams generally point to the hiding in plain sight algae. You need your AHA moment. Every inch is suspect until it's been cleaned / scubbed. Even the foam on the back of the weir door. Any crevices such as stair trim, auto fills, water features, every last inch.

There are always organics being introduced but not to the level of crashing a balanced pool. That's where your buffer comes in on top of the daily UV loss, on top of minimum.
#teamrunhot.

Sounds like a plan.

 

[TaylorN]

I’d X2 the leaving the cover off part. It seems like a lot of these “my SLAM never ends” posts always have the cover as a common theme and removing the cover many times solves the problem.

I'll give it a week before leaving the cover open. I want to see how much chlorine drops in the next couple days with the SWCG at 0%. I can always throw some more liquid chlorine in and bring it back up to 15+ fC and then scrub and leave cover open.

Thanks guys!

 

[generessler]

And I am using a syringe to take water samples to make sure the amount of water is exactly what is needed.

That's a 2-handed operation? Are you taking water from the surface? It's best to sample about 18" down or more to avoid getting top water where chlorine is depleted.

 

[TaylorN]

That's a 2-handed operation? Are you taking water from the surface? It's best to sample about 18" down or more to avoid getting top water where chlorine is depleted.

I appreciate you looking out! I can actually pull the plunger one-handed and always get a sample with my arm about elbow deep in the water, so about 14-18" deep. I then push out the excess water from the syringe with both hands.

 

[an1vrsy]

What is consuming chlorine?!? SWCG can't keep up. Been SLAMing. Crystal clear pool now. Never algae on walls .

UV and/organics consumes chlorine. You have a covered pool the majority of the time. So that leaves organics. SWG are designed to keep up with a set FC level, when utilizing the FC/CYA chart. Per this thread you've set your SWG + pump run time = FC 3.2 ppm

With your climate in San Diego a FC loss of 3.2 this time of year would be acceptable. Since your post doesn't show testing everyday, it is difficult to really understand your FC losses. Because your pool is covered the majority of the time, you feel the FC should keep rising because the sun (UV) isn't burning off the chlorine. Which leave organics.

You really need to perform an OCLT. With your cover open all night, test your FC level after dark and before sunrise. (yes, set an alarm and test before the sun comes up). I believe I read in this thread you did an OCLT and had a loss of FC greater than 1 ppm. Which means you have organics.

Any thoughts? Did I leave out any pertinent details? Should I be doing something differently?

Those were my thoughts. I have an autocover and I still keep my CYA in the recommended value range around 70 ppm. However, I open my cover most days between 12 pm to 6 pm. I am part of the #FCrunhot crew and keep FC around 8 - 10. Swim parties or not, FC has never dropped below minimum, that is why I have a SWG. Oh, btw, today mine is set for 24/7 33% which yields 3.0 ppm.