6ppm consumption or bad bleach?

[rjledoux]

My pool has been consuming around 6ppm bleach for the past month. Every day I've been feeding it 128oz of 10%. That's ~6.1ppm per poolcalculator.

Today I noticed what might have been algae on the light. I scrubbed it down and removed the light. Nothing behind the light. I decided to SLAM I had a couple of small spots a couple of weeks ago as well.

CYA is 45-50
FC was 5.4 to start + 1 bottle = target 11.5 one hour later
FC was 7.3 +1.9ppm so I've consumed 4.1 ppm in one hour? +1 bottle = target 13.4 one hour later
FC was 9.3 +2.0ppm so I've consumed 4.0 ppm in one hour? +1 bottle = target 15.4 one hour later
FC was 11.2 +1.9ppm so I've consumed 4.1 ppm in one hour?

The one bottle per day has been very consistent.

Is it possible that I'm not consuming at this rate and this is crapo bleach? That's only ~2ppm
my daily readings have been more or less consistent and the FC delta on a bottle is strangely consistent

1 week ago I passed an OCLT, I've never had CC > .5 and I can read the mfg of the drain cover from the deck.

If I hold here instead of going to 21 (target) for an OCLT what would this confirm bad batch of bleach? All of it came from the same store and was stored outside (not cool).

 

[JohnN]

That sounds like a lot of chlorine to lose. 2 questions for you, 1) What is your CYA and 2) What test kit are you using? That said, 10% loses strength more rapidly than 8.25% bleach, especially if it is stored outside in the heat, and even more so if it is stored in the sun.

 

[rjledoux]

and BOOM! 1.6 CC
Hello Mr. algae, I've been looking for you
Although I haven't ruled out that the bleach is weaker than 10% as well. I'm going to pick up some 8.25 from another source tomorrow.

 

[JohnN]

Ok, so you definitely have algae, but I think your bleach may be a bit weaker than 10% also, which wouldn't surprise me based on what you said about its storage conditions. I guess the combination of the 2 could cause your problem.

 

[rjledoux]

12am - 5am drop from 14.2 -> 12.6 on FC with CC at .9
It's clear something is consuming the FC but it's also clear that the bleach was not raising the FC as much as it should causing the numbers to look worse. I'm switching to cal-hypo tonight. I have enough room in my CH that this won't cause any issues.

 

[rjledoux]

When evaluating an OCLT, is it required that the pool be at shock level to declare a success? Is <1ppm FC loss good enough at 80% of Shock?

 

[duraleigh]

Is <1ppm FC loss good enough at 80% of Shock?

Absolutely.

 

[rjledoux]

Absolutely.

Done!

 

[linen]

Was the swg off when you did the OCLT?

What are you using for a test kit?

 

[rjledoux]

yes

 

[linen]

You might have missed my second question (I edited my post)...what test kit did you use?

 

[rjledoux]

normally I use a LaMotte 2056 but I use the FAS-DPD from a K-2006 when I expect FC to be above 10ppm.

 

[linen]

I am confused by your numbers above then:

2am - 5am drop from 14.2 -> 12.6 on FC with CC at .9

since the K-2006 either has 0.2 or 0.5 resolution. I would not trust the colorq for the OCLT or the <0.5 CC measurements...you are just asking for trouble.

 

[rjledoux]

I finished up with the FAS-DPD at 13.5ppm .5ppm overnight loss with <.5cc. The Colorq theoretically has a .1 resolution on FC but I can't get a source of chlorine consistent enough for me to validate the instrument. I doubt LaMotte's claim on that resolution. It's not bad for everyday testing but it's useless for SLAMming. For other tests it varied ~10% on CH and ~15% on CYA against the known concentration solutions I made.

 

[linen]

Good, just wanted to ensure you are really done with the SLAM process...your numbers with 0.1 resolution (resolution does not equal accuracy) made me wonder.

 

[rjledoux]

The numbers early in the thread were from the LaMotte or the LaMotte with 50% dilution. The variance was too high to be of any real use. I happened to see a K-2006 on the shelf when I picked up some Cal-Hypo. The LaMotte accuracy still doesn't account for the weak bleach. My 10% bleach was more like 3%.