Chlorine Nil - PH falling - TA rising

Problems relating to pH and total alkalinity.
Increase ph, increase TA. Reduce pH, reduce TA.
pH chemistry advice and techniques for the pool.
SamVimes
Pool Newbie
Pool Newbie
Posts: 2
Joined: Wed 13 Jun, 2018 10:37
My Pool: Small (7m x 3m) in ground concrete pool installed in 2007 with a vinyl liner (replaced in 2017).
Astral Sena pump and a sand filter - no pool heater installed. Pool is used for three months at a time - when in use it's vacuumed/backwashed/rinsed every day and chlorine/PH/TA checked every day.

Chlorine Nil - PH falling - TA rising

Postby SamVimes » Wed 13 Jun, 2018 11:06

Just opened the pool after winter - super chlorinated it and set the pump going. After a couple of days the water looks good and clear.

The problem is that the Aquacheck test strips are showing nil for the chlorine each and every day for the last five days despite twice adding enough dichlor to raise the reading to 10ppm.

The PH reads 6.8 and today fell to 6.4 despite adding Soda Ash (this is rare as we have hard water)

TA is has risen from 146 to 168 and now 180 (as it's a hard water area we have never had a TA reading below 120)

Each morning there are a couple of areas of brown deposits on the bottom. It's not sand so I assume it's algae. Added a treatment dose of algicide on day 1 followed by flocculant a day later. They keep returning.

After owning the pool for 11 years and managing to achieve good levels most of the time I am at a loss this time. Any ideas?


Denniswiseman
Swimming Pool Superstar
Swimming Pool Superstar
Posts: 961
Joined: Tue 06 Sep, 2011 05:48
My Pool: 10k inground fibreglass, Telescopic Cover, Hayward Powerline pump, Quality filter with glass media, 27kw output heat pump, K-2006C test kit
Location: United Kingdom

Re: Chlorine Nil - PH falling - TA rising

Postby Denniswiseman » Wed 13 Jun, 2018 12:33

Hi Sam and welcome
First of all chuck the strips and get a decent FAS/DPD testing kit (Taylor K2006c or TF100) strips and pool stores are widely inaccurate
Then check these numbers
FC:
TC:
pH:
TA:
CH:
CYA:

The Trichlor / Dichlor products you are using are elevating your Cyanuric acid and making your chlorine ineffective and reducing your pH
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

Once you know your CYA you can then reduce it to a more manageable level by partial drain and refill

Because of your algae you will then need to Slam with relation to your Chlorine / CYA Chart and recommended Pool Levels

You should then be able to keep your pool in balance with these basic products
Liquid chlorine (sodium hypochlorite or plain bleach)
There's a lot to get on with for now and feel free to ask more questions
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
Teapot
Swimming Pool Superstar
Swimming Pool Superstar
Posts: 418
Joined: Tue 17 Oct, 2017 10:52
My Pool: 12 x 24 (45m3) liner pool, Triton TR60 filter with AFM glass media (Activate) and variable speed pump running 0.08HP
Location: UK

Re: Chlorine Nil - PH falling - TA rising

Postby Teapot » Wed 13 Jun, 2018 15:00

Seconded!
Get the cyanuric acid stabiliser checked and definitely NOT with a test strip. You will always have problems as will most when using test strips, they could almost have been invented by the industry as a cheap way to create issues for owners that pool shops can solve.
In a vinyl pool hardness and alk are almost irrelevant.
SamVimes
Pool Newbie
Pool Newbie
Posts: 2
Joined: Wed 13 Jun, 2018 10:37
My Pool: Small (7m x 3m) in ground concrete pool installed in 2007 with a vinyl liner (replaced in 2017).
Astral Sena pump and a sand filter - no pool heater installed. Pool is used for three months at a time - when in use it's vacuumed/backwashed/rinsed every day and chlorine/PH/TA checked every day.

Re: Chlorine Nil - PH falling - TA rising

Postby SamVimes » Thu 14 Jun, 2018 00:50

Thank you to Denniswiseman and Teapot for your replies - Teapot you made me laugh out loud with your cynicism but you're no doubt right all the same. Denniswiseman I realise that I have just been very fortunate over the last few years and that actually I have a lot to learn. I understand the mechanics of the pool's pump and filter system but I have to take more time to understand the chemistry. I will read the links thoroughly. Thank you again
Denniswiseman
Swimming Pool Superstar
Swimming Pool Superstar
Posts: 961
Joined: Tue 06 Sep, 2011 05:48
My Pool: 10k inground fibreglass, Telescopic Cover, Hayward Powerline pump, Quality filter with glass media, 27kw output heat pump, K-2006C test kit
Location: United Kingdom

Re: Chlorine Nil - PH falling - TA rising

Postby Denniswiseman » Thu 14 Jun, 2018 02:13

It's great that you have listened and are prepared to change but your own FAS/DPD test kit will be the most important part of it and will allow you to keep your pool chemistry perfect
Teapot
Swimming Pool Superstar
Swimming Pool Superstar
Posts: 418
Joined: Tue 17 Oct, 2017 10:52
My Pool: 12 x 24 (45m3) liner pool, Triton TR60 filter with AFM glass media (Activate) and variable speed pump running 0.08HP
Location: UK

Re: Chlorine Nil - PH falling - TA rising

Postby Teapot » Thu 14 Jun, 2018 06:36

Can't over look photometers as well

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