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
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 » 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
Pool Industry Leader
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Location: San Rafael, California

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
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 » 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
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 » 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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