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 » 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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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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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.
wheelyjon
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Consistently high TA and low pH zero free chlorine

Postby wheelyjon » Sat 23 Jun, 2012 12:56

Thanks for your reply.
As the pool is indoors, it gets only sunlight through double glazed windows, but it is always covered with a white plastic roller cover, except when being used, so that may amount to perhaps 15 mins per day on average, or a bit more when it is warm weather (not this year!) DPD1 tablets give a good colour, but adding DPD3 makes no difference, it stays the same colour as with DPD1 only.
Regards John.
chem geek
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Consistently high TA and low pH zero free chlorine

Postby chem geek » Sat 23 Jun, 2012 13:28

Glass will block a lot of the UV in sunlight so that should not be a problem and your chlorine should not get depleted during the day even when the pool is uncovered -- that's why it is lasting so long. Sorry I wasn't more specific about that -- it's not sunlight in general, but the UV in sunlight that depletes chlorine.

So with DPD3 not changing the color, that means your Combined Chlorine (CC) is very low which is good (I think you should still get a good Taylor K-2006 or TFTestkits TF-100 test kit). Getting CC in indoor pools is not uncommon (so you're lucky so far) because there isn't the UV in sunlight to help break down some of the bather waste in the pool, most likely from breakdown of chlorine forming hydroxyl radicals that are powerful oxidizers. If you end up with a high enough bather load in your pool where you find the CC rising and/or smell disinfection by-products, then you may need to use a UV system to help control that. Just see how things go, but since your pool is indoors, you can use a low CYA level such as 20 ppm and have the chlorine be at least 10% of that level (up to 20% is OK) and this will be a MUCH better experience than most commercial/public indoor pools where they don't use any CYA.

Just remember that Trichlor and Dichlor increase CYA while Cal-Hypo increases CH so you'll want to use chlorinating liquid or bleach in your pool unless you have a saltwater chlorine generator.

My wife experiences this difference in active chlorine levels from CYA use vs. non-use every year where 5 months of swimming 3-4 times per week in an indoor commercial community center pool with 1-2 ppm FC and no CYA has her swimsuits degrade in one season, her skin flakier and hair frizzier. During the 7 month swim season in our own outdoor residential pool swimming every day with an FC that is around 10% of the CYA level, which has the same active chlorine level as a pool with 0.1 ppm FC and no CYA, the swimsuits have lasted for nearly 9 years and there aren't the problems with skin and hair. The difference is likely due to the 10-20 times difference in active chlorine levels.
wheelyjon
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Location: UK

Consistently high TA and low pH zero free chlorine

Postby wheelyjon » Wed 27 Jun, 2012 11:14

Great thanks so much for your help, we will continue as we are until things go wrong! I am now using Sodium Hypochlorite (14%/15%), but have some stabilized granuals to hand should I need to increase the CYA.

Regards John
Unk

Consistently high TA and low pH zero free chlorine

Postby Unk » Sat 07 Jul, 2012 10:17

Howdy guys, I've read the posts and tried to follow, but must admit I found myself zoning out. So here is my issue
- Have new intex style pool. (4,000gal.)
- After setting up and filling kids swam for a couple days
- Rain storm, decided I should add chlorine
- Added chlorine granules (HTH non-stabilized Hypochlorite) used according to shock guidelines (16 - 21 oz. per 10,000gal.) cut it in half and used 9 oz.
- Added (4) 1" Chlorinating tabs with stabilizer to filter/skimmer
Tested the next morning and had no Chlorine (Free) reading and no Stabilizer reading
- over all PH was 7.5 ; Total Alk. was 180
Added chlorine again, still no reading... however now Alkalinity was high 240, but PH 7.5
Looked online seen and read that alkalinity would level out naturally - Asked pool store if I should keep adding chlorine granules till I got a registered reading, they said yes.
Added again that evening.
Next day still no readings for free chlorine, but high Alk. and normal PH.
Called HTH - they said the problem was the pool Alk. and that I should add 13 oz. of PH Minus for 11 days, and that for future ref. I should only add 4oz. of Chlorine granules and two tablets for my pool. (after hanging up I wondered if that was daily, weekly, etc.)
SO I'm on day 4 of that - Now having ALK. reading of 180 - and a 6.4 PH
Should I begin to add chlorine again?
Should I just let it sit a day and let PH rise?
Should I.... grrrr, help!
Guest

Consistently high TA and low pH zero free chlorine

Postby Guest » Sat 07 Jul, 2012 10:19

Oh and Hardness was consistently 200- 400 range, still
chem geek
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Consistently high TA and low pH zero free chlorine

Postby chem geek » Sun 08 Jul, 2012 02:10

Are you sure you've got no chlorine? Maybe your chlorine level is so high that it is bleaching out your chlorine test. If you are using a DPD chlorine test where you measure the intensity of pink/red against a standard, then that can happen if the Free Chlorine (FC) level gets above 10 ppm. If you are using an OTO chlorine test where you measure the intensity of yellow against a standard, then that won't bleach out and high chlorine levels will look orange or even red in that test. The best test kit to get is the FAS-DPD chlorine test as found in the Taylor K-2006 or the TFTestkits TF-100.

So if you determine that your chlorine level is really zero, then add more. You can use The Pool Calculator to calculate dosing and can read Beginner's Guide for Seasonal/Temporary Pools if you intend to take the pool down over the winter.

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