Consistently high TA and low pH zero free chlorine

Problems relating to pH and total alkalinity.
Increase ph, increase TA. Reduce pH, reduce TA.
pH chemistry advice and techniques for the pool.
chem geek
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Consistently high TA and low pH zero free chlorine

Postby chem geek » Tue 12 Jul, 2011 21:02

Use chlorinating liquid or 6% unscented bleach. You don't want to use Dichlor or Trichlor since that will increase the CYA level (unless your CYA is now truly zero in which case you might want to use some, but not too much, Dichlor). If your CH is low, you can use Cal-Hypo if you prefer.

If you are free of ammonia, then that is hopeful. You can do a bucket test to see how much chlorine it will take where 1/4 teaspoon of 6% bleach in 2 gallons of pool water is 10 ppm FC.


wheelyjon
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Consistently high TA and low pH zero free chlorine

Postby wheelyjon » Sun 17 Jul, 2011 12:11

Here is the latest update. I put 10 l of 4.7% Sodium Hypochlorite into the pool, but by the next morning there was no free chlorine. I then added 2 lots 200 gm of Brichlor granuals, one in the morning and another in the evening. By the next morning there was a trace of free chlorine showing. Today I have added another 100gm of Brichlor. I normally use about 100gm a week, the pool is 28,500 l Should it really take all this chlorine, or is something else killing it?

Wheelyjon
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Consistently high TA and low pH zero free chlorine

Postby chem geek » Sun 17 Jul, 2011 20:17

If you are only losing chlorine during the day and not overnight, then your CYA level is probably low. I don't recall your testing it recently after this high chlorine demand incident. So you can either add some pure CYA or use Dichlor as your source of chlorine for a short while since for every 10 ppm FC it adds it will also increase CYA by 9 ppm.

By the way, there is Trichlor and Dichlor -- no Brichlor. If you meant Trichlor, then for every 10 ppm FC added by Trichlor, it will also increase CYA by 6 ppm and it's also very acidic so watch your pH.
wheelyjon
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Consistently high TA and low pH zero free chlorine

Postby wheelyjon » Mon 18 Jul, 2011 11:30

cancelled
wheelyjon
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Consistently high TA and low pH zero free chlorine

Postby wheelyjon » Mon 18 Jul, 2011 11:37

Sorry about the duplicate posts, but I could see them or your reply until I made another post.
Brichlor was the trade name of the chemical I used, but I see the latest pack is just called stabilised chlorine granuals (Di-chloro-isocyanurate, dihydrate). As you say strips are not very good for CYA, but they show either 0- or 40, both are pretty well the same colour. I contacted the email address you send for a better test kit, he replied that he was on holiday but would contact me on his return.
Thanks again for all your help, I hope the corner has now been turned
chem geek
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Consistently high TA and low pH zero free chlorine

Postby chem geek » Mon 18 Jul, 2011 20:40

For every 10 ppm Free Chlorine (FC) added by Dichlor, it also increases Cyanuric Acid (CYA) by 9 ppm. Your test strips are useless and I would not trust them at all, especially for CYA. It's not just their wide ranges, but they are simply not accurate. Please get yourself a proper test kit, either the Taylor K-2006 or the TFTestkits TF-100 .
wheelyjon
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Location: UK

Consistently high TA and low pH zero free chlorine

Postby wheelyjon » Sun 04 Dec, 2011 17:20

Earlier this year you gave me a lot of help with my pool. The problem finally turned out to be a CYA reading of 100ppm. As the pool was then warm and I did not want to dump water, I struggled on for the summer, but now the heating is off and the water cold and I am trying to decide what to do.

1. What is the best and cheapest way to treat the water in the winter (Indoor pool mosaic tiles with a roller shutter cover)

2. I have now started using 14%/15% Sodium Hypochlorite instead of Diclor granuals, how long can I keep this before it looses significant strength? (it is very expensive to buy just 20l at a time)

3. I realize that I do not full understand the function and chemistry of CYA, does it prevent free chlorine showing in tests?, or does it just make the free chlorine less effective. Is there anything available that explains how CYA works?

This is such a useful site, I really apperciate your help.
Wheelyjon
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Consistently high TA and low pH zero free chlorine

Postby chem geek » Mon 05 Dec, 2011 01:21

You will want to dilute your pool water to get the CYA level lower so that you won't have to have such a high Free Chlorine (FC) level. Since you've now already got CYA in the water, you can just use either chlorinating liquid or bleach, whichever is cheapest "per FC". Clorox Regular and most off-brand Ultra bleaches are 6% while chlorinating liquid varies but is usually either 10% or 12.5% or sometimes higher as in your case.

As shown at the bottom of this page , concentrated chlorinating liquid loses its strength faster though this is very temperature dependent. It also depends on the quality of the chlorinating liquid as any metal impurities can have it degrade much faster. You can see that even with good quality chlorinating liquid stored at 75ºF (about room temperature), that 15% strength will lose half its strength in 148 days (about 5 months). If you store the chlorine in a cooler well-ventilated garage or in a shed or outdoor box (unless you live in an area where it freezes), then it will last much longer.

With your pool water being colder, your daily chlorine usage should drop considerably so long as it is not exposed to sunlight (yours shouldn't be since it is indoors and has a cover). While such a pool if unused might use 0.7 ppm FC per day at 88ºF, it would likely use half that, or 0.35 ppm FC per day, at 75ºC and half again, or 0.17 ppm FC per day (1.2 ppm FC per week), at 62ºC.

CYA does not prevent chlorine from showing up in the FC test. Hypochlorous acid releases from being bound to CYA in less than a second so it measures as FC. However, it is the instantaneous concentration that is relevant for killing/preventing algae and killing pathogens. The releasing of more chlorine from CYA just prevents you from running out, but doesn't affect the kill rate. It's like having soldiers in hand-to-hand combat on the front line (i.e. active chlorine which is hypochlorous acid) while you've got a lot more chlorine in reserve as chlorine bound to CYA and as hypochlorite ion. When a soldier dies on the front-line, another in reserve takes his place, but the rate of killing has to do with how many front-line soldiers you have and it doesn't matter how many you have in reserve in terms of the rate of killing, though it does matter with regard to how long you can continue to fight (unless you add more soldiers -- i.e. chlorine). This thread goes into more detail if you are interested.
wheelyjon
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Location: UK

Consistently high TA and low pH zero free chlorine

Postby wheelyjon » Sun 17 Jun, 2012 05:21

You gave me a great deal of help last year when I had a high CYA problem. This year I started by draining most of the water and re-filling and I now use liquid chlorine.

CYA is now very low (<20ppm) and Chlorine has remained at about 3 for weeks on end. May I ask 2 question: 1. Is there any problem having a very low CYA? The water is clear and the chlorine seems to stay for ages.
2. I have tried DPD3 tablets, but never get any reading for total Chlorine. Is that correct or am I doing it wrong? I assume you add the DPD3 to the sample with DPD1 in it?
chem geek
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Consistently high TA and low pH zero free chlorine

Postby chem geek » Sun 17 Jun, 2012 19:05

The only problem with low CYA is that if the pool is exposed to sunlight then you will lose chlorine too quickly. Also, if the CYA is very, very low (near zero), then the chlorine will be too strong and will oxidize your skin, hair, swimsuits, etc. faster than is necessary and may produce more disinfection by-products as well. Generally, you want your CYA in the 30-50 ppm range unless you are in a climate with long hours of intense sunlight in which case an even higher CYA level is OK. Also, for saltwater chlorine generator (SWCG) pools, 60-80 ppm CYA is better since it reduces chlorine loss to sunlight allowing one to turn down the on-time of the SWCG. Since you say the chlorine seems to last, the pool must not be exposed to direct sunlight -- is that true? If so, then you can have a lower CYA level, but I'd shoot for something more like 2 ppm FC with 20 ppm CYA or 3 ppm FC with 30 ppm CYA. I wouldn't go below 20 ppm CYA since you can't accurately measure it.

If you got a proper test kit, then you use R-0003 reagent to measure Combined Chlorine (CC). It sounds like you aren't using a FAS-DPD chlorine test kit. Are you saying that you use DPD-1 and see a color to get an FC measurement but then add DPD-3 to that sample and it turns clear? That doesn't make any sense.

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