pH rising due to aeration?

[RGS]

I have seen posts on TFP saying that using bleach will usually not raise your pH, but that using tri-chlor tabs will usually lower pH (because they are so acidic) making it necessary to add pH increaser to counteract this.


My experience has been the opposite. Back when I was using Tri-Chlor tabs in an in-line chlorinator, as my main method, I found that pH stayed in the normal range 7.4 to 7.6 and that I very rarely had to add acid, and never had to add pH increaser.


Now that i am using bleach exclusively, I find that pH regularly rises, so I have to add acid a couple times a week. On average, I'm using about 1 to 1.5 gallons of 20 Baume muriatic acid per month, in a 16000 gallon pool. I'm not complaining, but am curious why my pH experience is different. The only explanation I can think of is aeration, since I've heard that tends to increase pH due to outgassing of CO2.


My pool has a waterfall from the spa with a 1 foot drop to the pool. Part of the return flow goes to the spa and part to the pool, and all the drainage is from the pool. I have a variable speed pump. I run it 10 hours a day on low speed plus 2 hours on high speed (to make my pool vac run effectively). So it gets 2 hours of fairly vigorous aeration per day.


I find that my TA is tending to go down, probably due to the regular acid dosing I have to do. My fill water has a TA of 100, and my pool TA is down to 60 now. Back when I was using tri-chlor tables and rarely added acid, I found that my TA tended to rise, and it was around 170 before I drained the pool and switched to bleach last spring.


just curious what everybody's thoughts are on this. I'm not bothered by this, other than the fact that I may have to add baking soda if the TA gets too low.

 

[camueller]

My thoughts are that you are seeing exactly what should be happening happen with TFP. Now that you've got your TA down to 60 you should see the pH rise slow down....but with a TA up at 100 or more that waterfall aeration is sure to cause pH rise. It wasn't a problem with pucks since they counteract this pH rise, but when you stopped using them you had to counteract it another way (MA). But if you have your TA at the right place you shouldn't have to add MA that often. And if you find yourself fighting high pH, the more you add acid the faster it'll go down, eventually bringing you to an equilibrium.

 

[VinDeeLoo]

Yes, the pH rise is due to aeration. Your TA is not affected by aeration, but lowers due to your MA addition.


Sent from my iPad using Tapatalk

 

[bdavis466]

Trichlor is net acidic and does a good job of lowering pH levels. It is not uncommon for chronic trichlor users to have their pH fall into the 4's and have a TA of 0. Did you ever add anything to increase the TA?

The process of adding liquid chlorine is basically pH neutral to very slightly alkaline. With that said, the switch to liquid chlorine is not the likely cause of pH rise in and of itself. Aeration speeds the process that dissolved carbon dioxide (carbonic acid) leaves the water and in doing so, results in a rise in the pH. Maintaining a higher pH (7.6-7.8) and a lower TA (50-60) combats this somewhat as at those levels produce an end result that is much closer to being at equilibrium with the carbon dioxide content in the air.

Unfortunately pH rise will always be an issue. You will never be able to stop it but can only slow/ lessen your acid additions.

 

[JoyfulNoise]

I find that my TA is tending to go down, probably due to the regular acid dosing I have to do. My fill water has a TA of 100, and my pool TA is down to 60 now. Back when I was using tri-chlor tables and rarely added acid, I found that my TA tended to rise, and it was around 170 before I drained the pool and switched to bleach last spring.


just curious what everybody's thoughts are on this. I'm not bothered by this, other than the fact that I may have to add baking soda if the TA gets too low.

It depends on what type of trichlor tablets you were using. Many of the "X-in-1" type tablets (take your pick, 3-in-1, 4-in-1, etc, etc) contain baking soda and/or soda ash (sodium carbonate) as both a way of cutting the tablet with a cheap binder AND reducing the pH drop since the net acidity of the trichlor will be offset by the added base. It's usually an attempt to make the chlorinating tablet pH neutral. SO, if one of those types of tablets is used regularly, I could easily see a net increase in TA over time.

This is why TFP teaches users to carefully understand what is in the chemicals they use and what those chemicals do. This way, one can not be surprised by "strange side effects".