Chlorine is disappearing!

[Youfah Mizzum]

Please read SLAM Process
You are not following the SLAM Process

I appreciate everyones input. I really do but I have read the SLAM process page a thousand times. And many other pages!
I'm quite familiar with it & could possibly repeat it verbatim.
I am 100% following it to the letter.

Your SLAM FC is 20 ppm if a CYA of 50 ppm.

Understood. I am well aware.
My CYA isn't 50.

Let me just repeat, yesterday I whacked in a big dose of chlorine to bring it up to somewhere around 5 to 8 ppm. Not SLAMming but a decent dose. I also tested CYA and it showed 40 to 45. Then in the evening I took a OCLT which showed 5 to 6 ppm. This morning at early light it was barely 1 so today I commenced the proper SLAM as per the process. But to be sure of the correct dose, I just verified the CYA and it showed 70. So I SLAMed according to CYA = 70 (Cl = 28 ppm).
PoolMath said to add 5L liquid chlorine. Done. Took a reading a few hours later & it showed CL at 36 ppm. Nice for SLAMing but yes too high & wasteful - I get it but that's what PoolMath said.

Scrubbed the whole pool surface, the whole skimmer box, skimmer flap, the water line (one of the advantages of working from home - not much work done today. Mostly spent in the backyard dealing with the SLAM)!
I've done my evening OCLT Cl test & will report back later on the mornings reading. Alas tomorrow I need to attend the office so can't be watching it like a hawk but will ensure the Cl is appropriate for the SLAM process in accordance with CYA level which I will also test in the morning. Might even read the SLAM page again for the 1,459 time. I can always get the wife to chuck in 500ml halfway through the day which will definitely keep it at or above 28 ppm. 500 ml might be overkill but Cl is cheap. Roughly $1 AUD per L.

Just a reminder - I'm not treating a disgusting algae bloom here. Water is crystal clear already. I am just trying to suss out why Cl is reading < 1 for the past several weeks. The OCLT showed algae hidden somewhere so it's not like Cl is getting consumed at some excessively quick rate. Today's SLAM might've sorted it already but will continue tomorrow.

Night everyone. Thanks for all your input, concern & helpful suggestions.

 

[Bperry]

Just a reminder - I'm not treating a disgusting algae bloom here. Water is crystal clear already. I am just trying to suss out why Cl is reading < 1 for the past several weeks. The OCLT showed algae hidden somewhere so it's not like Cl is getting consumed at some excessively quick rate.

Going from 4-6 or 8ppm to <1ppm overnight is a huge loss of chlorine! If it’s not green now, it will be very soon if you don’t keep on it.

It seems like you got most of the SLAM process down, but most newcomers miss part of it and it seems like you may be too, but it could just be that your a working stiff like most of us and can’t stay by the pool every few hours.

The M is for “maintain” and that means checking it and dosing the FC back up to SLAM level every single hour all day long (as a best case). Not many people can do that so TFP generally recommends at least several times throughout the day.

Waiting all day or until the next morning to check and re-dose is better than nothing, but it’ll take much longer that way.

 

[Youfah Mizzum]

Morning report:
CYA: 50
Evening pre-OCLT Cl: 30
Morning post-OCLT Cl: 25

So, yes some Cl loss. Note that is using a 5ml sample and 1 drop reagent = 1 ppm. Accuracy might not be quite as good as a 10 ml sample.

Comments: So yes I know the CYA change from yesterdays 70 is surprising, unusual, should be investigated et al. I'm very confident my CYA testing is fine so I doubt operator error. And I know I keep repeating this, but dropping CYA level for me has been normal since the pool was built. Maybe not to that degree (SLAM might have something to do with it?) but it typically drops anyway.

SLAM Cl at 50 CYA = 20 so I am already exceeding the required Cl level for SLAM. I therefore am not concerned that my absence today will impact the SLAM. If there is Cl loss through the day, I think it would only get down to SLAM level anyway. Just to be sure, I whacked in about 200ml of liquid Cl before leaving for work. So that will increase from 25 up to about 27. Plenty of room for it to drop through the day to 20.

I barely have sufficient reagent to do any more Cl testing, just another OCLT for night & morning test then I reckon it'll be gone. I do have a local pool shop which seems to match my tests within reasonable ranges so not the end of the world. Just a minor hassle and not quite the FAS-DPD standard.

 

[Newdude]

I do have a local pool shop which seems to match my tests within reasonable ranges so not the end of the world. Just a minor hassle and not quite the FAS-DPD standard

The problem with that is that they will tire of you testing without buying anything quickly. And, no, that cute little flamingo thermometer doesn't count. You also can't do either part of the OCLT with them because they're closed.

You get a good chunk of a free pass from me with limited testing options in Australia, but figure out a way to test at home because the SLAM needs tests that are far too frequent for the pool store.

Also, I'm not sure of it's been mentioned but you want to perform a full blown algae treasure hunt. With clear water and a large FC loss overnight, it's festering in plain sight. Light niches, ladder rails, auto fill, all up in the guts of the skimmer, etc etc etc. Every last inch is suspect until proven otherwise. It may be in more than one place even.

Keep us posted.

 

[Youfah Mizzum]

The problem with that is that they will tire of you testing without buying anything quickly.

LOL. Yep, but I get my Cl and acid from them so they still drain my wallet.

I'm not sure of it's been mentioned but you want to perform a full blown algae treasure hunt.

It has, and I have done a thorough scrub of the whole skimmer region. The door, the walls, the basket etc. It was all clean anyway but gave it a scrub with a nail brush anyway.
I don't have any ladder or hand rail (see my profile pic) but I do have one more pipe I can try to flush. Will do that tomorrow. This old thread is similar to my situation What to do with an unused pressure cleaner pipe?
I know...Should've mentioned it before but I completely forgot until half an hour ago. That I hope is the culprit!

 

[Mdragger88]

Very possible it’s the festering culprit-
Do you have a light?

 

[Mdragger88]

Also - did you check weir door foam? Like take it out & check the backside of the foam

 

[Youfah Mizzum]

Thoroughly checked those disused pipes & gave them a solid flushout with super chlorinated water. I can't do visual check but I'm so Dang persistent that I have no doubt that I flushed out anything that might've been lurking. And the SLAM water has floated back into the pipes anyway.
Skimmer weir door has no foam but everything has been scrubbed.
Just done my 2nd night OCLT (CYA seemed consistent with this AM reading at 50). Cl currently at 22ppm.

 

[aussieta]

Just done my 2nd night OCLT (CYA seemed consistent with this AM reading at 50). Cl currently at 22ppm.

oclt is done after sunset and before sunrise

 

[mgtfp]

Just done my 2nd night OCLT (CYA seemed consistent with this AM reading at 50). Cl currently at 22ppm.

That was a bit too early, more than an hour before sunset, still a bit UV around, even though not much. If you pass, then no worries. But if it's a close fail, then you have an inconclusive result.

 

[Youfah Mizzum]

oclt is done after sunset

That was a bit too early, more than an hour before sunset

Appreciate the sentiment behind those comments & grateful for the assistance but I am well aware of the SLAM process by now. Unfortunately my busy schedule meant I couldn't do the test after sundown but the aspect of my pool, neighbouring homes, hills etc means that my pool is fully shaded from 4:30ish pm. And it's covered. And it was overcast.
I 100% have no concern over the ambient UV.

 

[mgtfp]

It's not just the UV. Even in a fully covered pool you lose FC due to chlorine oxidizing things. That's for example the reason for CYA getting reduced without water getting removed - it gets oxidized by chlorine.

For this reason, the OCLT criterion is not zero FC loss over night. The normal overnight loss (without algae) depends on many factors like FC- and CYA-levels, temperature (chlorine oxidation rates double roughly every 13°F), or if there is a pool cover that adds extra oxidation surface. And of course time.

The 1ppm OCLT threshold has been chosen to cover a wide range of the above mentioned parameters, including typical times between sunset and sunrise in summer. If someone for example tells me that they had zero overnight loss while being at SLAM-FC, CYA 90 and 30°C water temperature, then I know that something's not right - with parameters like that it wouldn't be unusual to lose more than 1ppm even without algae, and we sometimes recommend in cases like that to do the OCLT with a lower FC.

If you add extra time to the required OCLT period, you will lose extra chlorine in that time and increase the risk that you get a false-positive result, and will have to go through another day of SLAM and another OCLT. Rather than doing a half-hearted OCLT, I would just keep slamming until I can do a proper OCLT.

I know that SLAM and OCLT are a pita. The only options you have is whether you want the pain to be short and sharp or long and just a little bit less sharp.

 

[Youfah Mizzum]

If you add extra time to the required OCLT period, you will lose extra chlorine in that time

Understood. Without a thermometer just arm in to elbow level & knowing by experience, my pool temp would be about 25°C - 26°C.

This mornings report:
nighttime CYA: 50
nighttime Cl: 21 ppm

Morning CYA: 50. Seems to be holding so for me that's a good result.
morning Cl: 21 ppm

CC has always been good but tested again just to be & sure enough, looks fine. And water utterly sparkling. It was clear before anyway but thats a KPI so worthy of a mention.

So by all measures, SLAM is over.

Just need to deal with those forgotten pipes - will never know if they were to blame but that's my suspicion.

My REAL measurement is setting my SWG back to 40% and seeing what the Cl reads at after a few days. Need to wait for the SLAM level to drop.
Might even get my delivery of Cl titrating reagent by then.

Once again, appreciate the virtual hand holding.

 

[Newdude]

Just need to deal with those forgotten pipes - will never know if they were to blame but that's my suspicion.

Sometimes the last thing you checked coincides with the timeframe the SLAM finished itself. Other times it *was* the last thing you checked.

We'll never know but it sure went night and day once the pipes were flushed, so I'll happily go with that too.

 

[mgtfp]

Looking good. My suggestion would be to do another OCLT with a 10ml sample once you have new reagents to be on the safe side. Doesn't have to be at SLAM level. I'd also recommend to stay a bit on the higher side of the FC/CYA chart for a while, like higher target end for liquid chlorine pools. Just to make sure to not slip too low until you found the right SWG settings for the "new" conditions where you are not losing chlorine like crazy. It's better to slowly approach your final target from above than doing an up and down rollercoaster.

 

[Mdragger88]

What are the unused pipes for? Can they be capped, drained, & isolated?

 

[Youfah Mizzum]

What are the unused pipes for? Can they be capped, drained, & isolated?

They were intended for use by future pool heating.
We did end up getting a heater but its inline with the filter pipes & pump.

I've capped what I can but the heater return pipe is at the bottom of a wall just a few cms up from the pool floor so I need to jump in and pull off the directional eyeball and whack in a cap. In the meantime I know the water inside is sanitised so not critical right now.
Today's gonna be a warmish day & the SLAM Cl level would've dropped more by the arvo so I'll jump in and try to deal with it.

 

[mgtfp]

Today's gonna be a warmish day & the SLAM Cl level would've dropped more by the arvo so I'll jump in and try to deal with it.

The pool is safe to swim in up to SLAM-FC, as long as the water is clear enough to see the bottom.

 

[Youfah Mizzum]

The pool is safe to swim in up to SLAM-FC, as long as the water is clear enough to see the bottom.

Clear enough? LOL it's Dang well like a diamond! Anyway, 30 seconds later and that pipe is capped too. The eyeball just slid right out and I inserted a rubber plug as tightly and best I could.
So all pipes capped.
Now just a waiting game. I'll keep an eye on the Cl levels and CYA levels daily & will do a OCLT maybe this time next week.

 

[AlexPowell]

You didn't check your main drain