Breakpoint Chlorinantion Question- help.

RockyStandish

Member
Feb 7, 2016
5
Providence, RI
I have a relatively new public indoor pool I'm managing. I have my cpo but am a bit rusty. So far things have been running smooth. But recently, a challenge came up.

We test the pool twice a day. Slowly, over time, the CC has steadily climbed. We try to shock it every 2 weeks or so by bringing the FC up to 10ppm. That always seems to help lower the CC, but never quite gets it much below 1.0 ppm. (state regs require .2ppm CC for public pool). We've been keeping CC somewhat at bay (1.5 or lower) but recently its really gotten away from us. Our CC levels are now a 4.84 (see all test results below). We've always done a "shock' (raise FC to 10ppm) but have yet to do a calculated "breakpoint chlorination". We've tried our traditional shock (2 bags Calcium Hypochlorite) again this past week with no success at budging the CC number. We also tried shocking with Sodium Dichloro a couple days later (using 5 bags per the pool stores recommendation, rather than the 2 bags it calls for on packaging). Still didn't move the CC. We tried Oxidizer a couple days after that, which seemed to help a little but primarily drove down FC without much of an affect on CC. We've gotten the pool water tested at our local pool store everyday. Even they are now out of options to help us. Their computer diagnosed 12 bags of shock based on test results below (again, normal amount for a pool our size per instructions on bag are 2) but they think that can't be right and is too much. From what I know and from my own research it seems we need to finally do a breakpoint chlorination. I have 2 main concerns:

1) Following the 10:1 rule of FC to CC for breakpoint, we will need to raise the FC to 48 PPM to hit breakpoint for a pool with 4.8 CC? that seems insanely high to me but I could be wrong. This would align with what the pool store's computer told us (12 ish bags of shock), but since that spooked them its obviously spooking me.
2) Our pool is a public pool open 7 days a week. Is 12 hours/overnight enough time for FC levels to get to a healthy place after being jacked up that high and allow us to open the pool the next day? I assume no way. So could I use Oxidizer after 12 hours to drive the FC levels down to a healthy place so we can open?
3) If we can do #2 and use Oxidizer to get FC levels back to a safe level, is 12 hours even enough time for breakpoint chlorination to occur and break down all that CC?

PS- other than CC, the pool water feels/seems/smells perfect. And even with the CC levels that high the ammonia smell is barely noticeable. We have a very strong hvac system which im sure hides what would otherwise be a strong smell. I've spent about 40 hours this week researching, studying, testing, asking and I can't seem to get a sold answer to the questions above. This site comes up the most when I do web searches for info so it seems to be an authority more so than any others. So I'm hoping you guys can help. Thanks in advance.

FC= 3.57 ppm
CC= 4.84 ppm
pH= 7.2
Hardness= 200 ppm
Alkalinity= 71 ppm
CYA= 30 ppm
Total dissolved solids= 5700 ppm.
 

JVTrain

TFP Expert
Feb 3, 2014
5,081
Central Minnesota
This site is primarily for home owners and the advice is tailored as such. I don't believe we are in the business of giving advice to public pool operators.

However, I'm very comfortable in saying it's simply unacceptable to be relying on pool store testing when managing a public pool. You should be testing your own pool water using Taylor reagents and a drop based test kit, not some magic 8-ball electronic pool store testing. Those test results aren't worth the paper they were printed on.
 

ewkearns

Well-known member
Aug 19, 2014
693
Shallotte, NC
Other points to be made, regardless of type of pool:

1) "FC= 3.57 ppm" is far to filthy to allow anybody to swim in it,

2) Nobody can manage any pool without a quality test kit.

You can, indeed, follow the recommendations found in this forum, when managing a pool of that size, if the bather load isn't very high..
 

RockyStandish

Member
Feb 7, 2016
5
Providence, RI
as I noted in the first line of my post- we test twice a day. we have a drop based kit. but we also bring to a pool store as an extra precaution.
noted on that article linked above and the re-assessment/modification made around the 10:1 logic. Whether I use the new type of measurement to reach breakpoint (10:1, minus number of already existing CC) or old (10:1) math seems to require that based on a CC level of 4.84, I would need to raise FC levels to north of 40ppm. Does that seem excessive? And if we were to do it, would oxidizer bring the FC levels back down to safe level?
 

ewkearns

Well-known member
Aug 19, 2014
693
Shallotte, NC

tim5055

Mod Squad
TFP Expert
LifeTime Supporter
May 11, 2014
10,377
Franklin, NC
Well, I would have a couple of questions.

What drop based kit are you using? A Taylor K-2006 I would hope.

I'm confused with your statement "state regs require .2ppm CC for public pool". Does New York require all pools to have CC in them? I'm going to assume you meant that the regulations do not allow CC higher than .2. If so, is your pool closed now?

Be careful with the Dichlor you have been using for shock. it will drive your CYA up quickly. Speaking of CYA, your listed level is 30 so if you follow our methods, your normel weekly shock has not even been getting to true shock level. For a CYA of 30, shock level is 12ppm FC.

Instead of throwing more chlorine shock at the CC, maybe you need to look at MPS as is discussed here: Chemistry of Chloramines - indoor commercial pool
 

ewkearns

Well-known member
Aug 19, 2014
693
Shallotte, NC
Since they are using "their test" and the pool store's test, I couldn't tell what came from where..... so, I just thought I'd throw that out there for good measure. You 're probably right, though....
 

dkjbama

LifeTime Supporter
May 7, 2012
20
Florence, AL
Shooting from the hip here; if I'm way off, someone please correct me. This is an indoor pool thus you don't have the benefit of UV from the sun to break down the CCs.You may need to use potassium monopersulfate (aka chlorine-free shock) to break down the CCs.

As has been said before, you need to do good testing with your own kit. When we see chlorine numbers reported down the hundredth of a ppm, we become suspect as the only thing that produces these type numbers are electronic whiz-bang gadgets the can't compete on accuracy and consistency with a simple titration test.

EDIT: Whoops, looks like its already been covered above, I just missed the MPS acronym.