Metal sequestrant chlorine tolerance

n240sxguy

Well-known member
May 17, 2014
1,802
Benton, KY
#1
Day before yesterday I came home to a freshly green pool. I opened it about a week ago with iron staining like I had last year. I added some hth brand metal sequestrant to give it a try since it was considerably cheaper than the Jack's I used last year. It removed the stains, and the pool looked great. I'd been adding a gallon of liquid chlorine a day while I was letting the filter and pool cleaner do their thing. Turns out I let my chlorine level get a little high since I was just adding a little liquid chlorine each day without testing, and it messed with the hth metal sequestrant I had put in it. Here's where it gets weird, at least to me; FC was 11.5 the day before yesterday with roughly 75 cya. I made sure the swg was off. Yesterday it was pretty and blue again with just a tiny bit of residual discoloration, so I figured the chlorine had dropped and the sequestrant was doing its job again. Well, the FC was still 11. Does this have more to do with the FC level, or the possible ph fluctuation based on that FC level? My ph was 7.5 when I opened the pool.


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pooldv

Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
Aug 10, 2012
24,993
DFW, TX
#2
Yes, it is more about the pH with iron and green water. FC sometimes will cause a pH bump that will make it seem like it is the FC level. I've seen quite a few times that 7.5 to 7.6 is about the cutoff point. The higher FC level can chew up your sequestrant a bit faster.
 
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n240sxguy

n240sxguy

Well-known member
May 17, 2014
1,802
Benton, KY
#3
Ok. So the higher ph caused it to break the bond with the iron, then as the FC came down, the ph also came down, and allowed it to re-bind with the iron? Hopefully this warm day today will burn off enough FC that I can get an accurate ph reading to verify.


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n240sxguy

n240sxguy

Well-known member
May 17, 2014
1,802
Benton, KY
#5
Ok. I was worried that the higher FC had just obliterated the sequestrant, and I'd have to add it all over again. I was relieved when it turned back to blue. Glad it's still there, and doing its job.


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n240sxguy

n240sxguy

Well-known member
May 17, 2014
1,802
Benton, KY
#6
Pool looks even better today. FC is 9, and ph is 7.2. I'm guessing the cya I added during all this dropped the ph. Surely a couple points of FC couldn't have raised it that much. The whole thing still seems weird, but at least it's back to looking blue.


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