PH went from 7.5 to <6.5 OVERNIGHT?! Help!

Problems relating to pH and total alkalinity.
Increase ph, increase TA. Reduce pH, reduce TA.
pH chemistry advice and techniques for the pool.
Terribly Inept
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PH went from 7.5 to <6.5 OVERNIGHT?! Help!

Postby Terribly Inept » Sun 24 Sep, 2017 03:02

Hi all, hopefully someone can help me as I am utterly bemused by what is going on with my pool chemistry.
My pool is 10,000 gallons. I use a palintest Pooltest 3 to read my pools levels, I use the manufacturer supplied reagents.

Around a month ago my pool had a free chlorine level of around 6ppm, way too high for an indoor pool. I left it open to the sun for a few days without any chlorine treatment and have had on going problems since then.

My pool no longer holds free chlorine. I've been using a multifuncation chlorine tablet that also contains an algaecide and a flocculant (200g, contains Trichloroisocyanuric Acid).
My chlorine level has been 'stable' at about 0.28 ppm. I have tried adding stabilized chlorine granules, in addition to the tablets and also Sodium Hypochlorite 14/15% (Liquid Chlorine). None of these have had any effect at raising the free chlorine levels in the pool. It stays at an avarage .20 ppm - .40ppm.

The pools Ph was low at 7.0. Over the last week I had been slowly raising raising the pH. Yesterday night it was a 7.5

Went to test the free chlorine and Ph levels today. My meter is reading a free chlorine level of 0.28ppm and a PH of less than 6.5. (just reads (<6.5).

How the heck did my pH level go from 7.5 to <6.5 OVERNIGHT? and why is my pool not holding free chlorine?

I last shocked the pool around 2 weeks ago.

Please help I have absolutely no idea what the problem is here.

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Re: PH went from 7.5 to <6.5 OVERNIGHT?! Help!

Postby Denniswiseman » Sun 24 Sep, 2017 15:03

Check your Cyanuric acid you may not be adding enough chlorine because your CYA is to high
An indoor pool only needs 20-30ppm CYA
Check out Chlorine / CYA Chart
For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm

The addition of CYA will cause your pH and TA to drop as will any acid
Can you supply a complete set of numbers
These common chemicals are cheap and don't add any unnecessary extras
Liquid chlorine (sodium hypochlorite or plain bleach)
Muriatic acid (hydrochloric acid) to lower pH and TA
Bicarbonate of soda to raise TA
Aeration will raise pH only
Soda ash will raise pH and TA

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