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.
wheelyjon
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My Pool: Indoor, covered with roller cover, mosaic tiled sand filter surface area 21 sq m volume 28,500 l
Location: UK

Consistently high TA and low pH zero free chlorine

Postby wheelyjon » Sat 25 Jun, 2011 07:06

My pool is indoors and covered except when in use, TA is 250, pH 7.1 and I cannot get any free chlorine. Any efforts to lower TA make pH worse and vica versa, the water looks ok, but a bit cloudy.
What do I do next ?


chem geek
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Consistently high TA and low pH zero free chlorine

Postby chem geek » Mon 27 Jun, 2011 21:27

Is your pool covered most of the time? Usually with that high a TA the pH will tend to rise over time, especially if there is any aeration. Is the TA of your fill water high? If not, then have you been adding baking soda (Alkalinity Up) -- just trying to figure out how your TA got so high. What kind of chlorine are you using -- is it stabilized -- Trichlor or Dichlor? If so, then your CYA level may be high making your active chlorine level too low. Trichlor is very acidic, for example, which would explain a lower pH, though usually the TA would be low as well unless you compensated for that.

Get yourself a proper test kit -- either the Taylor K-2006 or the TFTestkits TF-100 and then post your results here. In the meantime, you can try using chlorinating liquid or 6% unscented bleach as a source of chlorine to try and shock your pool to get the chlorine to measure. Note that if you are using a DPD chlorine test (the one where you compare shades of pink/red against a standard) that the chlorine could be too high and bleaching out the DPD test.
Guest

Consistently high TA and low pH zero free chlorine

Postby Guest » Tue 28 Jun, 2011 06:00

Hi.
Thanks for your reply. Yes I should give you a bit of history. When I opened the pool in April, I used about 4 l of Hydrochloric acid to clean the cover which had some scale on it. I then dumped about 1/3 of the water as the TDS was getting very high and re-filled it. I have just checked the TA of the tap water and it is reading 250, so perhaps this explains some of the high TA, I would have thought that the low pH would have helped bring down the TA, but at the moment I seem to be stuck with both values wrong and I cannot get any free chlorine in the water. Any suggestion as to how I can sort this out?

Thanks John.
chem geek
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Consistently high TA and low pH zero free chlorine

Postby chem geek » Tue 28 Jun, 2011 20:36

So with the TA higher you should be able to just aerate the water to have the pH rise on its own from carbon dioxide outgassing. That means keeping the pool uncovered. You can aerate by pointing returns up and running the pump on high so you create waves or break the water surface. If you have fountains, waterfalls, spillovers, etc. then running them will count for aeration.

If your pH tends to stay low or go even lower, then you may be using an acidic source of chlorine such as Trichlor tabs. If your Cyanuric Acid (CYA) level is high, then stop using such tabs. This is why I suggest you get your own good test kit so you can really know what is going on with your water. The high TA will only be a problem for scaling if your Calcium Hardness (CH) is also high (and pH as well) The main problem with a high TA is that it usually causes the pH to rise, but right now that doesn't seem to be your problem.

As for chlorine, it could be that it is high but you are using a DPD chlorine test which bleaches out at high chlorine levels. Or it could be that you've got nascent algae growth and need to shock the pool or your CYA is too high so the chlorine isn't able to kill such nascent algae fast enough. Or it could be that bacteria converted some CYA into ammonia when the pool was closed (if the FC got to zero at some point). Without numbers from a good test kit, it's hard to know what is going on.

You could try a bucket test taking 2 gallons of pool water and adding 1/4 teaspoon of 6% bleach at a time until you start registering FC. 1/4 teaspoon will be 10 ppm FC. If you've got ammonia in the pool, then this bucket technique will give you a rough idea of how much chlorine will be needed before you start measuring FC.
Guest

Consistently high TA and low pH zero free chlorine

Postby Guest » Wed 06 Jul, 2011 09:14

Hi Thanks for your suggestions.
I take your point about a better testing kit, but in the UK they seem to cost from about £100 (nearly $200). I have had the pool now for nearly 8 years, but this is the first time that I have had a bad problem. I looked at using bleach in a bucket, but the bleach we have does not indicate its chlorine content, so have put a small amount of stabilised chlorine granuals into a bucket of water. I normally add about 100gm to the pool every 4 or 5 days (pool is 28,500l)
In an 8 litre bucked I added 100mg which is equivalent to about 350gm in the pool, the next day there was no free chlorine showing so I added a further 50 mg, again the next day no chlorine was indicated, though there was a slight smell of chlorine when I first took the lid off.
The pool looks ok, though just slightly cloudy, but I do get scale and a slight green growth on the cover. The CYA in the pool shows 0 on the test strips. The only effective method of aerating the pool is to use the jetstream pump, however at the moment this is not working, but I hope that spare parts will arrive this week.
I am puzzled by the fact that a pH of 7.2 or less does not reduce the total alkalinity, also will aeration not also drop the pH?
Regards wheelyjon

Regards john
Guest

Consistently high TA and low pH zero free chlorine

Postby Guest » Wed 06 Jul, 2011 09:16

Hi Thanks for your suggestions.
I take your point about a better testing kit, but in the UK they seem to cost from about £100 (nearly $200). I have had the pool now for nearly 8 years, but this is the first time that I have had a bad problem. I looked at using bleach in a bucket, but the bleach we have does not indicate its chlorine content, so have put a small amount of stabilised chlorine granuals into a bucket of water. I normally add about 100gm to the pool every 4 or 5 days (pool is 28,500l)
In an 8 litre bucked I added 100mg which is equivalent to about 350gm in the pool, the next day there was no free chlorine showing so I added a further 50 mg, again the next day no chlorine was indicated, though there was a slight smell of chlorine when I first took the lid off.
The pool looks ok, though just slightly cloudy, but I do get scale and a slight green growth on the cover. The CYA in the pool shows 0 on the test strips. The only effective method of aerating the pool is to use the jetstream pump, however at the moment this is not working, but I hope that spare parts will arrive this week.
I am puzzled by the fact that a pH of 7.2 or less does not reduce the total alkalinity, also will aeration not also drop the pH?
Regards wheelyjon

Regards john
chem geek
Pool Industry Leader
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Consistently high TA and low pH zero free chlorine

Postby chem geek » Wed 06 Jul, 2011 23:53

Aeration raises the pH with no change in TA. Acid addition (or use of Trichlor pucks/tabs) decreases both pH and TA.

As for getting chlorinating liquid in the U.K., there are many different sources including Champion Liquid Ultrapure , Crown Liquid Chlorine and many others listed in this thread.

As for test kits, see if you can get a Palintest SP 315C along with the Palintest FAS-DPD SP 300 .
Guest

Consistently high TA and low pH zero free chlorine

Postby Guest » Mon 11 Jul, 2011 07:49

I already use a test kit with tablets for chlorine, pH and TA and have a meter for TDS, and also use test strips which include CYA, so am not sure that this kit would give me any more information?

Is liquid chlorine a more effective way of adding chlorine? Do you think it is now just a matter of adding enough chlorine, or can there be something else which is preventing free chlorine from showing on tests? I do not think it is a matter of bleaching from too much chlorine, as there is no smell of chlorine whatever a day after adding it.
I now have the jetstream working again and have done some aeration. the pH has possible risen a small amount, but not a lot.
Thanks again for all your help.
Wheelyjon
chem geek
Pool Industry Leader
Pool Industry Leader
Posts: 2382
Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

Consistently high TA and low pH zero free chlorine

Postby chem geek » Mon 11 Jul, 2011 14:13

Test strips are pretty bad for many of the tests, but are particularly bad for the CYA test. Odds are the CYA is not at all whatever your test strip is telling you.

As for chlorine tests, the FAS-DPD can measure up to 50 ppm and won't bleach out (you just add more powder if you see a flash of pink or think you have no chlorine) so is useful when shocking and can measure to within 0.2 ppm accuracy (normally you use a 10 ml sample for 0.5 ppm accuracy) which is useful for overnight chlorine loss tests.

If you have access to an inexpensive OTO chlorine test -- the kind where you compare the intensity of yellow against a comparator, then that will tell you for sure if you have any chlorine.

If your CYA level dropped and your FC level was zero for a time, then it's possible bacteria have converted some or all of the CYA into ammonia (or intermediate CYA breakdown products) which creates a HUGE chlorine (or other oxidizer) demand. This is described technically in this post and my personal experience with this is summarized in this thread . A bucket test will tell you how much chlorine you will need. You can also get an inexpensive ammonia test from a pet/fish/aquarium store, though 8-10x that amount is just a minimum of the cumulative FC that will be needed since there can be partially oxidized CYA chemicals that don't show up as ammonia.
wheelyjon
Pool Newbie
Pool Newbie
Posts: 9
Joined: Sat 25 Jun, 2011 06:59
My Pool: Indoor, covered with roller cover, mosaic tiled sand filter surface area 21 sq m volume 28,500 l
Location: UK

Consistently high TA and low pH zero free chlorine

Postby wheelyjon » Tue 12 Jul, 2011 11:04

Those are really interesting aticles, thanks for the links, I think I need to brush up a bit on my chemistry now! It looks as if I need to give it a pretty big dose of Chlorine, I will do more tests wit a bucket first. Is it better/cheaper to use a liquid Sodium Hypochlorite rather than Brichlor Granuals?
I got an ammonia test kit this evening, but it tests free of ammonia.
Wheelyjon

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