Balancing FC After Stain Treatment

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revitup

revitup

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Nov 30, 2019
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Pawleys Island, SC
Pool Size
8500
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Hayward Aqua Rite (T-15)
I’m trying to balance chems after a Jack’s stain treatment for iron scale (stain solutions #1&2). The program instructions say “This treatment can produce false free chlorine readings for 3-4 weeks. Use the total chlorine reading during this time.” Does that mean that I should regard my combined chlorine (CC) results as my FC number? Right now I’m chasing FC, can’t seem to get it to hold. My CC result is high. Don’t know quite how high as I haven’t put enough R-0003 in to get the solution to turn clear. It’s at least 4 ppm though. Does this mean that my FC is at least 4 ppm and I will have to work with the CC number to monitor FC for the next few weeks?
 
Jack’s #2 chemical is, I thought, sulfamic acid. If so, their instructions are wrong - sulfamic acid causes false high CC levels. But the CC’s created by sulfamic acid reacting with chlorine do have sanitizing effects. So you should simply not try to worry about the CCs for a month or so. Just get a total chlorine reading.

FYI - you do not add R-0003 to make the solution clear. You add the R-0870 to make it pink then to titrate with the the R-0871 drops until clear. That number of drops is FC. Then you add 5 drops of R-0003 to make the CCs show up as pink and then titrate again with the R-0871 to determine the CC levels.

Alternatively, if you’re only interested in TC, then add the scoop of R-0870 powder, add 5 drops of R-0003 and then titrate with the R-0871 and that number you get will be Total Chlorine (TC).
 
I guess I could use one more reassurance. This morning’s test, FC=.5, CC=11.5, so TC=12. My understanding is that indicates actual FC=12? The pool is safely chlorinated?
 
Did not see the question … sometimes I don’t get notifications.

No, your FC is ACTUALLY 0.5 and it will be difficult to keep it much higher than that. Your CC’s are high because the chlorine is mainly reacting with the sulfamic acid forming N-chlorosulfamates which show up as CC. As long as you have an appropriate amount of CYA in the water (30ppm should be sufficient), then you can swim. You’ll need to be very consistent and regular with your testing so that you keep an good level TC in the water while the sulfamate slowly burn off.

If this was iron staining the. I’m not sure why Jack’s would call out the use of sulfamic acid. Ascorbic acid works fine on iron and there’s no issues with CCs being artificially high.
 
Thanks for the reply. Now I’m confused though. Jack’s instructions imply to use the TC reading as the FC reading during this time. My CC (TC) readings for the last 3 days:
Tue. 12.0
Wed. 10.5
Today 8.5
FC tests at 0, even hours after adding liquid chlorine, it doesn’t hold a FC reading.
Aren’t the CC readings above equivalent to FC, just chemically affected to look like CC?
Isn’t the daily CC daily reduction noted in my readings above indicative of daily FC loss?
Is the daily FC 0 reading indicative that the pool is unprotected? Should I just be dumping liquid chlorine into the pool everyday? Even though it tests 0 a few hours later? How much?
 
I’m not using sequestrant. If stains reappear, they do, I’ll consider maintaining with sequestrant next time.
My other levels are normal, including PH at 7.4. My Poolmath logs are shared.
I kept adding liquid chlorine before I realized it was never going to hold. My TC was 21 before I realized that was the equivalent FC so looks like I hit SLAM level once already.
My CYA is 70 so my plan is to maintain TC (CC) as I would for FC with that CYA level (min 7 ppm) until FC starts holding. As long as that takes. Does this seem like the right plan?
 

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Ok, let's just take a pause and review some basic chemistry terms here because the terminology is getting flung round and used the wrong way. Also, whatever the Jack's Magic stuff says, ignore it for now, it's not helpful and it's oversimplified which is leading to more confusion.

FC is FREE CHLORINE. Free chlorine is only - hypochlorous acid (HOCl), hypochlorite anion (OCl-), or chlorine bound to CYA (CyaCl). Right now you have NONE of that in your water.

Sulfamic acid is an organic acid that is mainly used to dissolve hard-to-remove COPPER stains. Why it was suggested to you to use that for IRON stains is beyond me. Iron is typically treated with ascorbic acid.

When you add chlorine (bleach, SWG, trichlor, whatever form it is) to water that has sulfamic acid in it, the chlorine reacts with sulfamic acid to create N-chlorosulfamates. These compounds do have sanitizing/disinfection properties but they are considered SLOW sanitizers, so they are not exactly adequate for a pool that really requires a FAST sanitizer, ie, any of the free chlorine compounds I listed above.

When you test for the presence of chlorine in your water, you will find that you have no free chlorine but you do have a type of combined chlorine (CC) in the form of N-chlorosulfamate. It is a lousy oxidizer and it is a slow sanitizer BUT, because you added sulfamic acid to the water, it is all you will have until the chlorine (and UV from the sun) starts to convert chlorosulfamate into chloride (ie, salt ion) and sulfates. That process of degrading sulfamate take a LONG time ... can be weeks or even months.

Had you used ascorbic acid, none of these problems would be occurring.

So, your only option is to keep adding chlorine and pretend that your total chlorine level (TC = FC + CC) is doing the best job possible to protect you and your pool from algae. You need to keep your pH on the low side (7.4-7.5 is fine) and you need to slowly add chlorine until you start seeing your FC increase and hold. Right now you will see no FC for the most part and everything will be CC (N-chlorosulfamate). Hopefully that will be enough to keep the algae at bay. No guarantees.

As for staining in general, keep in mind for the future that you should not use sulfamic acid unless the stains are copper. And in that case it is often easier to dissolve copper stains and then dump the pool water to get rid of the copper rather than deal with sulfamic acid contamination. When the stains are caused by iron, it is much much easier to use ascorbic acid since the water will recover very quickly from that and you will get FC to hold once all of the AA is neutralized.
 
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Thanks for the input, everyone. Seems like I’m always going where no man has gone before - and shouldn’t! Lol. I’ll update when I see anything good happen.
 
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So here I am, 4+ weeks after stain treatment, and my FC and CC still will not test properly. Started out at the beginning of this fiasco with test readings of 6 or 7 TC (FC of 1 and CC of 5 or 6). Now weeks later, my test readings are FC=1 and CC=1. I have my SCG output at my normal setting for this point in the season, 20% (tested and I have FC=4 at the returns) and I’m spiking it with 16 oz of 10% liquid chlorine daily. The pool is clean and clear but, obviously, I have no idea if it’s sanitary.

Talked to a Jack’s rep and he’s baffled. He says, because I did not use sequestrant, the iron in my water is neutralizing my chlorine. Even though my pool tests 0 iron. All he could suggest is that I add sequestrant. I highly doubt that is going to fix the problem but I have no idea what to do at this point other than dump this water and start over. I can’t believe I’ve gotten myself into this fix. I’m desperate now and I am open to any and all suggestions.
 
You used sulfamic acid … what you’re seeing is totally normal when sulfamic acid is added to a chlorinated swimming pool. I’m not baffled at all … and yeah the whole “ iron is eating your chlorine” line is BS.
 
So all of a sudden today, FC is testing/registering normally. 38 days after the Jack’s stain treatment. Nobody is happier than me this morning.
For the record, TC - actually CC - was registering initially but, after about a week, testing was registering essentially 0 FC, 0 CC. I left the SCG set at normal output for this time of season and dumped in 1.5 ppm liquid chlorine everyday as ‘insurance’. Pool stayed clear the entire time.
Hope this helps someone dealing with this issue the next time.
 
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