Here is a link to a paper on the myth of lowering TA by the 'slug' or acid column method. Interesting reading!
http://www.poolhelp.com/JSPSI_V1N2_16-30_AcidColumn.pdf
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Here is a link to a paper on the myth of lowering TA by the 'slug' or acid column method. Interesting reading!
http://www.poolhelp.com/JSPSI_V1N2_16-30_AcidColumn.pdf
The paper EXPLODES the myth.
But they don't really tell us how to actually lower T/A, unless it's buried in the chemistry jargon.
Still, it's nice to have hard science yet again backing us up.
I get parts of that. But it seems to indicate that we get CO2 at pH of 8.3 or below, and we reduce pH to below 7.2 to have CO2 to off-gas by aeration.
I understood that no significant off-gassing/pH increase occurs above 7.2.
Is it that the concentration above 7.2 simply doesn't allow for the removal of CO2?
There actually are differences between dissolved CO2 and carbonic acid, but for the purpose of lowering TA we can pretty much ignore them. Several factors need to be taking into consideration for the rate of offgassing of CO2 and it gets quite complicated . CO2 can exist in the water at pH higher than 7.2 but for efficient offgassing having the pH low helps. Keep it simple since what you want to do is effeciently lower the TA. The method of dropping the pH and aerating works! Dropping the pH is what lowers the TA. Outgassing teh CO2 raises the pH without raising the TA back up. By having a lower pH you will have more CO2 in the water. If you don't lower the pH you can outgas CO2 and cause a pH rise but you have not lowered the TA, only raised the pH.
This table that I posted earlier in the Pool Water Chemistry thread shows how "out of equilibrium" a pool is at varying TA and pH levels. You can see that there is nothing magic or special about a pH of 7.2 but that you get further out of equilibrium at the lower pH which means that there will be faster net outgassing rate ALL ELSE EQUAL (i.e. aeration, surface area, wind, etc.).
In fact, if it really took a pH of 7.2 to cause the outgassing, we wouldn't be seeing SWG pools with rising pH problems above that pH, but we do. Also, the aeration effect to make pH rise wouldn't work above 7.2, but it does.
Richard