High PH, Low Alkalinity

[Phil.c]

Since shocking my pool, the chlorine shot off the scale, I've now done three partial water changes which still has the chlorine on high but the PH is now down to 7:8, however the Total Alkalinity is down do 21, do I now raise the Alk with chemicals or do another partial water change to get the chlorine down first?

[Denniswiseman]

The chlorine will come down by itself

Use these common products to balance your pool
Liquid chlorine (sodium hypochlorite or plain bleach) Liquid chlorine only adds salt
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

So use Bicarbonate of soda

[Phil.c]

Thanks, I understand that Bicarbonate of soda will also slowly raise PH, considering that my PH is already 7:8, do I lower this first?

[Denniswiseman]

To lower pH you need acid but that will lower TA and pH
Just use Bicarbonate of soda
Use Pool Maths to work out how much to add
If your pH rises use acid then add more Bicarbonate of soda
Testing is the thing

[Phil.c]

I've now risen the TA to the correct amount, checked everything else and they're all in the right scale

The filter is clean and the water crystal clear, I do however get a small amount of brown dust along the bottom corners, vacuuming it gets rid of it for a short time but it eventually comes back, I'm guessing that it's the sand media (new sand) not being fine enough the hold it, this is with 1200 rpm water circulation. This has always happened for the past twenty five years, it's always been dispersed by using the pool, this year the pool hasn't been used, so it collects.

[Teapot1]

I've now risen the TA to the correct amount, checked everything else and they're all in the right scale .

The industry likes a higher TA as it makes people buy more pH minus as their pH will rise. In short the industry is looking after itself and not your pool.
Depending on the contruction of your pool, vinyl and fibreglass can run lower TA at 40-60ppm and will not have a pH rise for ages, I run mine around 45ppm and havent added pH minus in years. Plaster/tiled pools can run higher at 60-80ppm and still remain stable just run a slightly higher pH 7.8 to compensate for the slightly more aggressive water.

[Phil.c]

My TA is actually at the low end of the scale and PH 7.8 so in your range. The pool has not been used this year.

[Teapot1]

Thats good Phil, your pH should stay pretty stable but at least you know how to counter it in future.