Chlorine is disappearing!

[Youfah Mizzum]

You didn't check your main drain

Main drain? What do you mean?

 

[Mdragger88]

Do you have a drain in the bottom of your pool?

 

[AlexPowell]

In your profile picture there is what I am assuming to be a hole with a cover - I went over the thread and this was not listed in the places you cleaned!

 

[Youfah Mizzum]

there is what I am assuming to be a hole with a cover

That is a hydrostatic valve. There's definitely not enough ground water pressure for that to have any bearing whatsoever.

 

[mgtfp]

That is a hydrostatic valve. There's definitely not enough ground water pressure for that to have any bearing whatsoever.

Is that visible round plate itself the valve, or is it just a cover and the valve is underneath? That's what I have.

My cover broke last year and when removing it to put a replacement in place all the disgustingness got revealed. Up to that point I had never looked under that cover in the 6 years or so we lived here. And I suspect the previous owner also didn't, so there was probably nearly 40 years worth of gunk accumulation.

Now I have a yearly inspection and cleanout under the cover on my pool schedule. Just did this year's and it looked quite reasonable - a few leaves and some dirt, nothing too bad. But I certainly don't want to let it accumulate again.

 

[Youfah Mizzum]

Is that visible round plate itself the valve, or is it just a cover and the valve is underneath?

No idea.
It's spotlessly clean and never even knew I could possibly remove the round plate. I daren't not remove it and I can't see how anyway.

So it's been a couple of weeks since the final OCLT and completion of the SLAM.
Pool has been spotless, wonderfully sparkling water - BUT still losing chlorine!

I just did another OCLT today and yes - the two tests showed a net loss of chlorine.

So, back to square one.

Just to repeat and summarise:
Have had the pool just over two years, newly built.
Up until around November last year, I'd always set the summer SWG generation to around 30% - 40%. Running about 8 to 10 hours a day. And that proved to be to the ideal level to maintain Cl around 3 to 5ppm. It is only a small pool, roughly 22,000 litres.
Always covered with a Abgal pool cover.
Winter time SWG is set to 5% and 8 hours.
Last November, had a minor algae outbreak following a huge windstorm that blew in lots of leaves.
Whacked in a load of chlorine and it cleared up over a few days. Basically a SLAM but without the close monitoring (yeah I know you peeps will say thats not a real SLAM and you need to be monitoring closely, doing OCLT, checking every few hours etc, but when it comes down to it, a SLAM is just a massive dose of chlorine maintained over a few days - which is what I did).
Since then, I can never take my eyes off the pool chem levels.
The chlorinator, even running at 95% over 11 hours cannot maintain a decent chlorine level. If I did that previously the Cl level would be north of 10ppm!
Thinking the SWG was faulty, I had it replaced under warranty. Made no difference.
So a couple of weeks ago I did a proper SLAM. It was a full 3 days. And the final OCLT showed a nil loss overnight. As an aside - I think the first time I cleared up the algae mentioned above I actually used even more chlorine over those few days - so actually the proper SLAM used less chlorine that what I did last Nov.
Now I find I am needing to supplement my SWG with about 500ml to 1 litre of liquid Cl each week. It just seems wrong and not what I have been used to for the past couple of years.

No other chemicals have been added to the water.

[ As an aside, I also discovered from this thread that my constant topping up of CYA is odd too. Apparently it's normal (for everyone else) that CYA is fairly constant once the target level has been reached but that has never been the case for me. I've always needed to top up CYA, so for me that is normal. Case in point - 6 days ago the CYA level was around 55. Measured it just now, it's 30. I'd go through a 2 kg bag over about 6 to 8 weeks. ]

About the only thing I can think of is theres a dead body inside the filter media! Obviously not, but really there's nothing else I haven't checked. Every nook and cranny has been scrubbed, SLAM hasn't made a difference. I use a skimmer sock so only minor debris gets past the sock and into the filter anyway.
Even the pool cover has been thoroughly cleaned as it was also in place during the SLAM, and even bleached a bit.

Methinks I need an expert chemist with a wider range of tests than just is what available to the average punter. Or maybe I need a voodoo shaman. Something is odd and I can't work it out.

 

[aussieta]

does anybody else in the household take any interest in adding chemicals
with the oclt, are you testing 1 hour after last chlorine addition or "assuming you added 4ppm of chlorine, so value should be X

 

[AlexPowell]

So lets recap - what is happening with salt levels?

 

[jklocke]

Here are a couple of thoughts I had as I was reading through your problems:

Have you always used the same brand of CYA? Maybe there is something off with the CYA itself?

What are your actual chlorine levels? I know your CYA is bouncing all over the place. What level of FC are you aiming for? Don't be afraid to let it run high, especially when the pool is still acting like there is algae brewing.

What are all your other levels - PH, TA, CH, CC, Salt? I don't think I ever saw anything listing all of those.

And following up on what @aussieta just said - are you testing 30-60 minutes after your additions to ensure they are getting your FC to where you think it is?

 

[aussieta]

what is the useage of the pool
young teenagers doing cannonballs when you are not home
and then filling the water back up so you dont notice
can you list the actual products you use
ie hyclor stbilizer or bioguard or whatever
can you try to keep your test results in your poolmath log
or at least list every result with each post
especially with who tested you or pool shop
just reread whole thread, post 20 you cannot take a water sample the night before taking to pool shop as fc and cc will not be accurate

 

[mgtfp]

Have you tried an OCLT with cover on?

The only thing I know of that is literally eating CYA is a type of soil bacteria that converts it into ammonia. But it doesn't really fit in your case. For those bacteria to thrive you need FC zero. And the ammonia would basically annihilate any added chlorine within half an hour.

After a successful OCLT you could also do an overnight chlorine gain test to verify that your SWG really is producing enough. Test FC after sunset. Then let your SWG run on 100% until just before sunrise, then test FC again. Compare the gain with what you'd expect (use PoolMath to calculate generated chlorine from SWG percentage and runtime).

Or do you have little kids that discovered that not going to the bathroom helps avoid FOMO? In your 22000 litre pool, 1 cup of urine eats about 1ppm of FC.

 

[mgtfp]

just reread whole thread, post 20 you cannot take a water sample the night before taking to pool shop as fc and cc will not be accurate

Good catch. OP said chlorine loss was 1ppm. In fact, it would have been much more, as the night reference sample also lost FC between taking the sample and doing the test.

 

[Youfah Mizzum]

with the oclt, are you testing 1 hour after last chlorine addition

No. I am testing at night. Last chlorine addition might've been hours prior. No one else touches the pool.

what is happening with salt levels?

Salt is very steady. around 5000.

Have you always used the same brand of CYA? Maybe there is something off with the CYA itself?

Yes I have and now you mention it, quite possibly the CYA isn't the highest quality. Way back 2 yrs ago when the pool was new I could get granular CYA from the pool shop, it was actually kinda flaked. But they don't stock that anymore. It only comes in large tabs/blocks. So I've been purchasing CYA from my local hardware shop which is powdered.

What are your actual chlorine levels?

Usually hover around the 1 to 2 ppm. My aim is consistently get around 4 to 5 ppm. I don't get 4 to 5 unless I add Cl.

What are all your other levels - PH, TA, CH, CC, Salt? I don't think I ever saw anything listing all of those.

All other levels are spot on. Ph = 7.2 to 7.6.
TA = 85
CH = 300-350 ish
Salt = 5000

young teenagers

little kids

Ha! No. It's just me & my wife. We're in our 50s & kids have left home.

can you list the actual products you use

All chemicals from Bunnings Warehouse, so Hy-Clor Stabilizer. Hy-Clor Calcium Increaser.
Local pool shop liquid chlorine and liquid acid (SwimArt). Here in Aust we don't use muriatic acid, it's hydrochloric acid.

Have you tried an OCLT with cover on?

Yep. In fact the OCLT from a couple of days ago was with the cover on.
That post I made about taking a sample to the pool shop was just to see if it correlated with my own tests. I realise I can't take that that test too seriously.
Now I have plenty of reagents I don't really have a pressing need to get tests done elsewhere.

 

[aussieta]

i use hy-clor from bunnings and dont have any issues, so we can eliminate that as a possibility
i cant see anywhere if you have autofill
how often do you backwash filter and then top up water
i only add cya after winter rains, and the most i have ever needed (this year) was 1.5kg, that is it for 12 months
ps bunnings sells hydrocloric acid in timber yard
i am focusing on the cya loss, because i think the answer to that is going to solve your fc loss
maybe take some water to your local aquarium shop and get tested for ammonia and nitrogen
tell them it is tropical fish. not salt, salt aquarium will be 35.000ppm
again please try to make it easier for us to find your test levels
i have to keep going back reading pages of posts to see where you are at

 

[AlexPowell]

You are not following the SLAM process because you're not maintaining the shock levels until you pass the overnight chlorine loss test.

Until you do this you're going to continue having this problem. It's not a matter for any advanced chemist. Salt levels are staying the same so there no no leak or dilution, the CYA is random up and down so is a red herring.

 

[Youfah Mizzum]

To all who have commented on the post, I am declaring this sorry saga over.
Not because I have it beat & have my answer - more because it's got me beat and baffled.

You are not following the SLAM process because you're not maintaining the shock levels until you pass the overnight chlorine loss test.

Not sure where you read anywhere that I wasn't maintaining shock levels until passing OCLT. I was and did.

Just to recap, this started back in Nov 2022 when I needed to jack up my SWG chlorinator production to maintain any semblance of FC. Prior to then, my summer settings were 35% running about 9 or 10 hours split between day and night. It seemed to start after a nasty wind storm blowing in lots of leaf litter. Coincidence? Who knows.

Since then, this thread documents my efforts to understand why.

I found that even running at 80% it was barely registering FC - even though my water was clear & no sign of algae. Nevertheless I did a SLAM strictly according to the documented procedure despite some here thinking I didn't.

Right now, I can maintain a FC level at around 3ppm (CYA between 50 to 60 maintained by adding roughly half a cup a week) by running the SWG at 100% for 13 hours/day, 8 hours during the day, 5 hours at night. And a reminder, this is a new chlorinator as my last one was replaced under warranty with the assumption that the saga was due to faulty gear. If I need to increase the chlorine, I'll just chuck in some liquid chlorine.
All other levels (salt, CH, TA, Ph et al) are all good and within recommended range.

So, after much testing and experimentation I'm just accepting that a switch was flicked last year and now my SWG needs to run at 100% for 13 hours a day.
Really appreciate everyone who have contributed to this thread.
It remains a mystery.

 

[mgtfp]

The cell that got replaced on warranty, had that recently replaced an older SWG? Could it be that you now simply have a smaller capacity cell than you used to have before?

The SWG from your signature should create 15g of Chlorine gas per hour. That gives you 15/22=0.68 ppm of FC per hour in your 22000 L pool when running on 100%. Over 13h that should give you nearly 9ppm. Let's say the cell is only 80% efficient, then it should still produce about 7ppm.

I'd suggest the following:

Confirm in night 1 that you have no overnight chlorine loss (OCLT).

Then in night 2 you do the opposite: Test FC at sunset. Then let the SWG run on 100% overnight and test FC again in the morning. Compare with what you would expect over the time the SWG ran over night.

If both tests turn out OK, then low CYA sounds like the only reasonable explanation. But according to your logs you added about 125ppm worth of CYA to your pool in the last month. I don't know how to explain that apart from a leak.

Or your neighbour doesn't like you and keeps pouring Peroxide into your pool?

 

[Mdragger88]

To all who have commented on the post, I am declaring this sorry saga over.
Not because I have it beat & have my answer - more because it's got me beat and baffled.


Not sure where you read anywhere that I wasn't maintaining shock levels until passing OCLT. I was and did.

Just to recap, this started back in Nov 2022 when I needed to jack up my SWG chlorinator production to maintain any semblance of FC. Prior to then, my summer settings were 35% running about 9 or 10 hours split between day and night. It seemed to start after a nasty wind storm blowing in lots of leaf litter. Coincidence? Who knows.

Since then, this thread documents my efforts to understand why.

I found that even running at 80% it was barely registering FC - even though my water was clear & no sign of algae. Nevertheless I did a SLAM strictly according to the documented procedure despite some here thinking I didn't.

Right now, I can maintain a FC level at around 3ppm (CYA between 50 to 60 maintained by adding roughly half a cup a week) by running the SWG at 100% for 13 hours/day, 8 hours during the day, 5 hours at night. And a reminder, this is a new chlorinator as my last one was replaced under warranty with the assumption that the saga was due to faulty gear. If I need to increase the chlorine, I'll just chuck in some liquid chlorine.
All other levels (salt, CH, TA, Ph et al) are all good and within recommended range.

So, after much testing and experimentation I'm just accepting that a switch was flicked last year and now my SWG needs to run at 100% for 13 hours a day.
Really appreciate everyone who have contributed to this thread.
It remains a mystery.

After looking up your unit I noticed some possible settings that correlate to the results you’re experiencing
This is supposed to be the approximate output for the unit you have,
set as you have it (I had to convert from g/hr to #/day)



Then I read this


Is it possible that you have one of these modes enabled?
If so, The resulting production would look like this

When you were manually dosing what was your daily fc consumption/loss?

 

[aussieta]

sorry to see you give in
but without accurate test data supplied
we can only guess

 

[mgtfp]

After looking up your unit I noticed some possible settings that correlate to the results you’re experiencing
This is supposed to be the approximate output for the unit you have,
set as you have it (I had to convert from g/hr to #/day)

View attachment 473845
View attachment 473848
Then I read this
View attachment 473849

Is it possible that you have one of these modes enabled?
If so, The resulting production would look like this
View attachment 473850
When you were manually dosing what was your daily fc consumption/loss?

That is a great find, @Mdragger88. This cover mode would explain a lot. 80% general reduction for a cover sounds a lot.