FC vs PH

[Theone01]

Hi all. Great forum to learn. Thanks.

While my ph was 7.6 and CYA~50, I let my FC get down to .8. I added too much 10% CL at once. About 1/2 gallon. My ph rose to 8.0 while the FC was 5.2.
The ph setteled down to 7.6 as the FC fell to 4.

Is that normal?

 

[Texas Splash]

Is that normal?

Welcome to the forum! It is normal for pH to rise temporarily when the FC level is increased, but typically the increased pH is observed when the FC is 10 or more. There may be a slight increase at lower levels, but an FC of 10 is where we caution members to understand the pH is going to climb then fall back down. Your numbers were much lower so I wouldn't think you should experience such a change. Perhaps the change you observed had something to do with the dosage/testing intervals, sample locations, etc?

But as a new member, I would encourage you to review our ABCs of Pool Water Chemistry if you haven't seen it already, and make sure to save/review those Vital Links below in my signature. Great to see you already have a K-2006 and are on top of things. Of course stay close to the [FC/CYA][/FC/CYA] to keep the FC balanced with your current CYA, and have a great weekend.

 

[tim5055]

Welcome to the TFP pool! :splash:

Totally normal.

We tend tol say that the use of liquid chlorine products is a pH neutral event, but you need to understand the chemistry a little. Matt says it best here:

Adding bleach to water can cause a temporary increase in pH which is usually offset by the chlorine reacting with organics and biological matter which are acidic (creates a proton) reactions. Thus, on balance, the net chlorine reactions are pH neutral. Most retail and commercial liquid chlorine products contain a small excess of lye from the manufacturing process but this amount of OH- is minimal and does not change the pH with normal levels of liquid chlorine use. If one were to add significant amounts of bleach (for example, raising the pool water chlorine concentration to shock levels), then the pH rise would need to be offset by an initial lower of the pH with acid. This is why TFP requires a pool owner to adjust their pH down to 7.2 prior to starting a SLAM.

So, a large addition of chlirne will produce a pH spike, but that will quickly come down as the chlorine reacts with stuff in the water.

 

[Theone01]

I thought so. I should mention the high ph reading was 15 minutes after I added the chlorine