FC sun loss during SLAM?

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gazelledrp - I have my fingers crossed. This is actually my second SLAM, did one earlier this year but I stopped after about 5 days. My testing then was even worse than it is now, huge variability in results and I don't think I was ever sure I passed an OCLT. Got close, like this time, and I think I just assumed it was good enough. Now here I am a couple of months later having to do it all over again, and I remind myself of my earlier failed SLAM to keep me motivated to get it fully this time....!

Unfortunately ran out of R-0871 this morning and couldn't find any locally. Replacement should be here tomorrow I think, in hindsight I probably should have ordered 2 kits! Anyway tonight I dumped 2 gallons into the pool - I've been using about 1.75 gal/day up to now based on my calculations - so hopefully it should stay up near shock level until I can confirm it with testing tomorrow. Also it can work it's magic at full strength during the night time.
 
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I'd really like a Mod to comment on the margin of error in testing at high chlorination vs. the 1ppm OCLT loss. It would seem that you would need to be shocking at 10ppm or less to have your margin of error and OCLT criteria fall in line such that the end result would be meaningful. Or perhaps modify the SLAM instructions to state for those with high CYA/shock levels: SLAM for 1 week, let your chlorine drift back down to 10, perform a OCLT, and go from there?

I don't know.
 
I've been reading a bit more on the margin of error and one tip I'm going to try tonight (when my new reagent arrives) is to use a medication syringe to more consistently measure my 10ml water sample. Right now I just pour from my water sample bottle and eyeball the level, so that may reduce one of the variables. Next, make sure there's definitely enough powder (2 heaping scoops it seems). Not sure how I address the final variable (drop size) except to try and be as consistent as possible. I did read that 24 drops = 1ml so if I could find an accurate enough 1ml syringe I could use that and calculate the equivalent number of drops....then again the first time my wife saw me using my Test Kit and SpeedStir at the patio table she commented on how it looked like I was setting up a drug lab so not sure how suspicious she's be about me ordering a ton of medical syringes. Especially when you factor in recent bulk purchases of bleach and hair nets (as disposable skimmer socks) :D.
 
We have had extensive discussions, theories and testing regarding the OCLT over the years. 3 ppm and up is the concensus for efficacy of the OCLT. There should be nothing consuming FC at night so it should not drop any no matter where it starts. Drop tests tend to be +/- 1 drop or less. Consistent measurement and technique is always important in testing. You can always use a 25 ml sample and count each drop as 0.2 ppm FC for a more precise test. For drops, be sure to hold the bottle vertically and give the drop time to form and drop onto it's own, don't squeeze too much.
 
I understand the principle of the OCLT - makes perfect sense. But at such a high drop count for those with high CYA, it seems perfectly reasonable to me that replicating 58 or 60 drops each test would be something of a stretch. And if the 10% variance is accurate/true, it just seems to me that the higher your CYA the more apt you are to run a SLAM much longer than you might need to.

I'm a newbie here so I'm sure I'm entering waters best left to the pros here. And I mean no disrespect or anything like that. The science oriented part of my brain is just struggling with it. If the SLAM level of chlorine is 10 or 12 or something low, I can make peace with it much easier/faster. 60 drops is a LOT of opportunity for variance and 10% of 60 is 6x's the OCLT fail limit. To my layman's eyes it seems like the deck is stacked against you if you're running high CYA (like us SWG folks).
 
Ok, my replacement reagents arrived today so I'm back into monitoring mode. Here's what's been transpiring since I ran out of reagent on Tuesday morning.

Tue 5am FC 14 (failed OCLT, loss of 1.5). Added 2 gal 10%
Tue 9pm added 'blind' another 2 gal 10%
Wed 6pm FC 15.5....little lower than calculated. 4 gallons theoretically adds ~25ppm, means I lost over 23ppm over 37 hrs. I was expecting 20ppm loss based on prior days testing (9ppm loss through each of the 2 daylight periods and 2ppm over the 1 night). Added 1 gal 10% at this time.
Wed 8:30pm FC 19....wait a sec. Didn't I just add 6ppm 2.5 hrs ago? Why did I only gain 3.5ppm? Anyway, added an extra gallon 10%. Brushed thoroughly, emptied skimmers (including dead frog) and removed the pool vacuum for the OCLT
Wed 9:30pm FC 22. Ok something's not right. 2 gallons added in the last 3.5 hrs should have added >12ppm but I only gained a little over half that in FC.

So I have something going on with the chlorine addition. I'm waiting 1 hr after addition, with the pump running 24/7, before taking my sample, so I don't think it needs more time for circulation. I went back and looked at my (large and growing) stash of empty liquid chlorine bottles in my garage. Unfortunately I can't remember which bottles I used this evening, but 2 of the bottles had date codes in the 30s and 1 was in the 60s. The remainder were all in the 160s and 170s.

So question - is chlorine 5 months old likely to have degraded to 1/2 strength? It's the Walmart 10% stuff, I assume it's been stored inside, so wondering if it's typical to degrade that much. If so that may have been the source of one of the smaller than expected additions this evening - likely the last one - but not sure about the other as I think I used a newer bottle.

And referencing our discussion earlier. When I started using the new bottle, I could have sworn the drops looked larger than the last one. I read the thread on the wrong nozzle tips being supplied so I checked that and it seems I have the right nozzle. So then I did a comparison step with a 1ml syringe and the results were pretty close - 44 drops with the bottle, 1.8ml x 24 = 43 drops with the syringe. Harder to tell the color change with the syringe, I found. So anyway I think I have confidence that my drop testing is pretty close. Will try the syringe test tomorrow morning as a comparison.

One other change tonight - I hadn't really been brushing the floor of the pool as I have a vacuum, but wondered if there was algae on the floor (I sure can't see it) and it had formed a biofilm, maybe the vacuum wasn't able to disturb it enough to let the chlorine get at it. I thought what the heck and brushed it tonight for the first time.

Anyway onwards and upwards to yet another OCLT. My water is crystal clear in daytime, but with my lights on after dark, I can see floating particles in the water close to the lights. Don't know what it is, maybe it's algae, if so I don't know where it's coming from but it's got to be dead by now, surely. Anyway 8 days now and counting now for what seemed like a very minor algae problem.....
 

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You can search the forum for bleach degradation tables, and yes, it's measured in months, and depends on temperature. Always get the freshest you can.

Glad you checked the nozzle tips and also found comfort on drop size.

Yep, scalp the algae everywhere, and no, you won't always see it, so the entire pool surfaces need to be brushed to speed things up.

I have my own opinions about high FC testing and the OCLT, but I can assure you that you'll know when you get close and you'll know when you have the algae beaten. You're getting lots of tests under your belt giving you the same experience we all work with. Sorry for the confusion on drops and errors. It's a debated topic here, everyone is volunteers, and instructions are written as best they can be. The key thing is that you will have zero loss of FC in the dark for a clean pool without algae, provided there is no other incoming organic contamination such as bather load, leaves, critters, teenagers sneaking in, etc.

Ask anything any time, and we'll stay focused on your SLAM. MMMaintain!
 
s1njin said:
Perhaps I misunderstood: http://www.troublefreepool.com/content/215-FAS-DPD-Chlorine-Test


  • The precision of the measurement is plus or minus one drop when up to 10 drops of titrant are used, or plus or minus 10% of the final reading, when more than 10 drops of titrant are used.

If I'm reading that wrong, by all means that's great news; but this is where I got that piece from. Am I in left field?
Click to expand...

We have discussed editing that. If you have further questions on this please start your own thread we need to stop hijacking the OP's thread.
 
Must say as the OP I have appreciated all the insights and contributions to this thread (hat tip to needsajet who's hung with me through it all). I know we've strayed into areas that have probably been debated at length many times before, but having the discussion in one place helped me get a much better understanding of the testing processes and improved my own confidence level.

Thanks for the pointer on bleach degradation. I went and read one of the threads with degradation.....wow. I've been buying 10 gallons at a time and storing it in my garage....guess that isn't a good idea, it gets >100F in there! Might explain how some of my losses have seemed higher than expected - at least one of those bottles sat cooking in my garage for 2 weeks after sitting on a Walmart shelf for 5 months - that 10% was probably 8% when I bought it and maybe as low as 5% a couple of weeks later when I put it in the pool. Coincidentally, yesterday I went back to the Walmart where I think I got that older stock and except for a couple of June bottles which I bought, the rest was all date coded February or March. I have another Walmart close by, and will make sure to check the date codes on every bottle and only buy what I need. Another learning!

Anyway, drum roll, onto the results of my OCLT. I think I may have passed, finally, maybe. My first drop test gave 18.5, drop of 3.5ppm overnight....cue curse words. Decided to try my 1ml syringe again - it gave FC 21.5 (1.8 ml, 43 drops) same as last night. So I repeated the drop test twice more and got FC 21 and 21.5. CC's <0.5 still and water as clear as ever, so I believe I am very close. I'm going to maintain close to shock level today, brush again tonight and hopefully another OCLT tonight will confirm.

Tfaff - welcome aboard and hope you can make sense and get some useful insights among my ramblings. It probably will take longer and more effort than you expect but stick with it, you don't want to have to do this again!
 
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Hey that's great news. :) Well done.

All going well, you get a little break as the FC comes down, which is the only candy or gold stars I have to offer, haha.

When you get a chance, post a pic! And not to rain on anyone's parade, but CC's are good right?
 
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Good good :) But it's also correct for me to say that you've met the OCLT criteria, so you are done either way!

<--- And hey, cool new badge over there under your handle! Thank you so much for becoming a supporter :)

Now as to syringes, I can handle mayhem, but when it comes to the word syringe, I look away. So I missed your CC and pool clarity comment. I just re-read it, and as long as your method is consistent with respect to the two FC tests for the OCLT, there's no logical problem with it. I do suspect you'll be doing a lot of explaining around here if you mention it too often :) But it sounds useful and inventive to me.

Anyhow, thanks again for your support and kind words, and good scrubbing the decks with you!
 
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Yeah the reason for the (I won't say the word) method was simply to try and be as consistent as possible measuring my water and my R-0871, but also provides a useful check against the drops. I usually find it helps to remove myself as a variable ;).
 

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