Re: Ph to low
This sounds right to me. Although I will note that we are in the spa forum here. Running the air jets happens, so the water comes into equilibrium with atmospheric co2 quickly. So long at the the PH is allowed to stabilize in between corrections, washing soda, baking soda, even 20 mule team borax, it doesn't matter, they ALL raise PH because they raise alkalinity.
As the pH rises from aeration, the rate of outgassing slows considerably such that, on any realistic time scale (most people don't soak for more than hour or so) this would not likely happen. One would need to have very low TA values and high pH to get to a point where the water was in equilibrium with atmospheric CO2 but then they would be in danger of having their TA crash followed by a crash in pH.
I agree that those chemicals do affect TA and pH. But there are ways to change pH quickly and ways to change pH without affecting other parameters. TFP always tries to recommend methods of chemical additions that have the fewest/least-complicated side effects. Adding baking soda to raise pH is a slow process that requires aeration in order for it to work. We have had many users who accidentally had low pH water and added lots and lots of baking soda only to see very little change in pH. They then wonder why this does not help them even though the "covential wisdom" (aka, "look it up on Google") tells them it should. They are missing the key ingredient necessary to make that happen quickly (aeration) and then they're annoyed because the pH hasn't budged much and their TA is now sky-high. So TFP tries to help people in the most efficient way possible which is to use aeration or borax to raise pH.
Even in a pool, all the PH threads here on TFP deal with PH GOING UP, not down. That's because the pools are out-gassing co2, to the atmosphere. All the advice on the issue deals with coming into equilibrium, IE letting lowering total alkalinity until PH stops going up.
Not true. Many users on TFP experience falling pH as well. This is typically seen in vinyl pool where the source water is acidic. Pool water almost never comes into equilibrium with atmospheric CO2 levels. If you look at
this chart you will see that a pool with 50ppm TA and a pH of 7.7 still has twice as much dissolved CO2 relative to atmospheric levels.
Adding bleach or fresh water causes alkalinity to go UP, and that is why PH is always rising in PH threads on TPF.
The only time PH is low here on TPF is because dry chlorine products being used are effectively acid, which LOWER TOTAL ALKALINITY WHICH CAUSES PH TO DROP.
Adding bleach does not raise alkalinity in any permanent sense. Bleach added to water initially raises pH but all chlorine reactions with biological and organic compounds are acidic so the pH rise is offset completely. There is a small amount of excess lye (NaOH) in all bleach that is used to stabilize the hypochlorite anion, but this does not add to the alkalinity in any meaningful way. The amount of hydroxyl anions (OH-) added is trivial when you consider the volumes of bleach added with respect to the total pool volume.
See this post for details on bleach chemistry.
The image that I linked to is neither confusing, nor irrelevant in any way.
It is confusing not because it is incorrect, but because it uses terms like "Elevated", "Normal" and "Deficient" CO2 levels without defining what those are. It also reports alkalinity in units of
meq/L which is not a term anyone using a pool test kit would know (it's a unit of measure chemists like to use to simplify the math) and it shows a pH range far above what would be found in typical pools. So, in terms of overall usefulness to a forum full of pool owners, it has little technical value.
