Ph and Alk.....a team???

[sunnydee]

Bear with me, as I ask all of you another monotonous chem question. Does ph and alk work as a team...meaning, do they both go up and down together? My alk was fine , but my ph was high. So, I added ph down and now I notice that my alk is moving down too! Whats's up with that? Geesh.  

[ssbraun]

Not to worry ...total alkalinity will come down with ph down products, but can be raised to proper range by adding household baking soda...this will raise TA without affecting ph much.

Steve

[HotTubMan]

What he said.

[fletch49]

...if your TA is really high (160-180+), then you will have a difficult time reducing your pH.

So, if your always adding pH down (as in my case), and it's not working, then try reducing your TA first, then your pH.

[ndabunka]

...if your TA is really high (160-180+), then you will have a difficult time reducing your pH.

So, if your always adding pH down (as in my case), and it's not working, then try reducing your TA first, then your pH.

 

Interesting recxommendation.  Now, EXACTLY how do you reduce TA without also reducing PH?

[Soakin]

Interesting recxommendation.  Now, EXACTLY how do you reduce TA without also reducing PH?

Wait, I know this one!

Sodium bicarbonate (baking soda) raises TA more than pH, sodium carbonate (soda ash)raises pH more than TA, and sodium bisulfate (dry acid/pH Down) lowers both.  Therefore, sodium bisulfate buffered with sodium carbonate should lower TA but not pH.

Now, if fletch49's pH needs to come down anyway, I'm not sure why you'd want to do it, but it is theoretically possible.  In sunnydee's case of normal TA/high pH, sodium bisulfate buffered with sodium bicarbonate is the way to go, as the original responses indicated.

I'm guessing that fletch49's point about reducing TA is that it acts as a pH lock, and you have to get rid of the excess TA before the pH starts to move -- but as far as I know you do that by adding pH Down.  My water starts out extremely high pH/TA.  It takes a lot of dry acid (24 oz)to get the pH to move.   After the water is balanced, I can adjust pH with a tablespoon of whatever is called for.  If I need to raise pH (like after an unbuffered MPS shock), I use soda ash to avoid raising TA.

[fletch49]

thanks Soakin...

You explained what I was getting at...TA acts as a pH lock, and if you are having difficulty reducing pH, it's likely due to  high TA.

In my experience, when I finally get my pH under control, I've basically dropped my TA to an unstable level (causing pH fluctuations), so I then need to use Sodium bicarbonate to then raise pH.

I have found it difficult to break the relationship between TA and pH.