Link between the TAL levels and amount of soda ash needed

[PerfectPools159]

Hi There,
I have been using the PoolMath Calculator and I am trying to understand the link between the TAL levels and the amount of soda ash needed to raise the pH.
What I discovered is that the higher the Tot Alk the more soda ash I need (quantity) to bring the pH up to my target levels.
My understanding was that if your TAL was already high the pH would tent to follow ie - move high.
Question - Why do I need so much Soda Ash to bring my pH up when it is so close to my target. see below example.

50,000 ltr pool
pH reading / Target / Soda Ash

6.8 / 7.2 / 1879 grams

--------------------------------------------------------------------------------

Alk Reading / Target

120 / 120

Hope someone can shed some light on this for me.

 

[BoDarville]

Re: Link between the TAL levels and amount of soda ash neede

Welcome to TFP!

Total alkalinity (TA) indicates the water's ability to buffer pH changes. Buffering means you need to use a larger quantity of a chemical to change the pH (up or down). A higher TA generally provides more buffering. While it is normally true that higher TA causes the pH to drift up, this does not appear to be the case with your pool.

A couple of other alternatives to raise pH with less of an impact to TA:

1. Add some aeration to the pool to raise pH without raising TA. Aeration exposes more of the water to the air. There are various ways to add aeration: fountain, waterfall, splashing, air compressor blowing air into the water, aiming return eyeballs towards the water surface so that more water breaks the surface, etc. Aeration increases the amount of CO2 outgassing, which causes the pH to go up without affecting TA. Don't have a waterfall or fountain? These post show some examples of homemade aerators: http://www.troublefreepool.com/my-aerator-t7799.html#p62236, http://www.troublefreepool.com/my-diy-aerator-t21867.html#p180448, http://www.troublefreepool.com/aeration-and-ph-t2228.html#p73794[/*:m:319ajdsv]
2. Use borax, or sodium tetra borate pentahydrate, to raise pH instead of using soda ash. The borax will raise pH while not raising TA as much as soda ash. [/*:m:319ajdsv]

 

[linen]

Re: Link between the TAL levels and amount of soda ash neede

Welcome to tfp, PerfectPools159

Since your ph test reads 6.8, you actual ph might be lower since most ph tests indicate 6.8 even for lower ph readings. Because of this, you should probably actively raise it with chemicals (preferably with Borax, but soda ash if you can't get borax quickly) until it reads at least 7.2 instead of the slower approach of using aeration to raise it.

How are you chlorinating your pool?

 

[PerfectPools159]

Re: Link between the TAL levels and amount of soda ash neede

HI Guys,
Thanks for the replies. To answer linen question. I am chlorinating via a salt chlorinator.

thx Adam

 

[linen]

Re: Link between the TAL levels and amount of soda ash neede

It is strange that your ph is so low since your relatively high TA and the swg should both cause your ph to rise. What is your fill water ph and TA?

 

[Smykowski]

Re: Link between the TAL levels and amount of soda ash neede

Do you have a test result history?

I agree with linen on the short term issue. Your pH is likely well below 6.8, so you're not really moving it four points, you're moving it more (and remember, pH is a logarithmic scale). Plus, your high TA is buffering that upward movement.

The bigger question is how it got that low in the first place.

 

[PerfectPools159]

Re: Link between the TAL levels and amount of soda ash neede

The pool is owned by a new customer of mine who's pool we have started maintaining.
After more probing she informed me that she went overseas for a while and used a heap of tablets in floaters to keep the pool from going green while she was away.

Guessing this is why the pH has dipped.
I will add the required Soda Ash to bring the pH back to what it should be.

Thanks again for all the help guys it has been invaluable.

Should of joined TFP a long time ago..