Drastic ph drop after aging.

[dirtyplants]

As for whether the pH can really rise and fall that "drastically", just recall grade school chemistry: You can titrate the pH of pure water (i.e. "soft") with mere drops of HCl or NaOH because pure water lacks buffering capacity. If your water is soft, and temporary agents were used to raise the pH, it is certainly conceivable that your soft water will revert quickly to its natural pH once those temporary agents dissipate during aeration/aging.

myofibroblast thanks for joining in.

This makes sense to me and was my visuals on this. Still the question is what are they are using to bring the ph up with.

[myofibroblast]

NaOH may have this effect but it's not the only additive that can have this effect. Remember it doesn't take much NaOH to raise the pH from 7 to 8 (which really isn't THAT drastic from a non-biological perspective). Fresh addition of NaOH to pure water, for example, can change the pH quickly. Think of aqueous solution of NaOH. If you make a 0.1 molar aqueous solution of NaOH, the pH will be 13 or so. You leave that 0.1M solution bottle open to the air, I can guarantee it won't be 13 for long. NaOH will most certainly react with dissolved CO2 (captured from air dissolved in aging water) and one ends up with less and less NaOH over time in an aged solution that is open to the air. In this case, the "solution" just happens to be your tap water.

Remember aging water is not just a single process of "degassing CO2" and driving out gaseous chloride. It is but one or two of the many chemical events happening. While most people will notice a rise in pH with aging water, some will not. I find it helpful to understand principles behind general rules. I think general rules are very helpful and often offer good guidance, but if one doesn't understand the underpinning concept, one cannot formulate a reasoned hypothesis to explain contradictory findings to general rules (or how to handle observations that contradict a general "rule-of-thumb").

[myofibroblast]

myofibroblast thanks for joining in.

This makes sense to me and was my visuals on this. Still the question is what are they are using to bring the ph up with.

I think the original poster should just ask their water treatment professionals whether they add sodium hydroxide or similar agents to the tap water. I'm not sure why they are so tight lipped about this, since it should be public information. Maybe they are just busy? Who knows. Or try the quarterly municipal water report from the city government if one such exists.

[Cichlidcraze]

Thank you Dirtyplants and Myofibroblast. That makes alot of sense to me. I feel i now have a much clearer understanding of the science behind the water aging process. I also googled this, but i dont think i was asking the right questions.

Cass

[dirtyplants]

The sodium hydroxide absorbs the co2 from the air which raises the ph temporally? Is that far too simplistic to say?

where were you when I was taking chemistry?

Thanks everyone here, you have indeed helped me with understanding water chemistry. I really appreciated this lesson as well as the original poster.

[Cichlidcraze]

Myofibroblast.

Are you by any chance a teacher? Cause i agree with Dirtyplants, that was really well explained.

ps. I dont believe that the water sanitation manager is too busy. I am probably just speaking to the wrong person. All the info wrt water perameters and quality, is posted on the national website. Now that i have a better idea of what i am looking for, i may be able to find it. Just for interests sake i want to mention that our tap water here in Cape Town is of very high quality.

Cass

[myofibroblast]

Cass, no, I'm not a chemistry teacher. I just enjoy science and nature! Currently I'm a little occupied with my new fish, which is turning out to be a bully! Some things nature can't change...

[myofibroblast]

The sodium hydroxide absorbs the co2 from the air which raises the ph temporally? Is that far too simplistic to say?

where were you when I was taking chemistry?

Thanks everyone here, you have indeed helped me with understanding water chemistry. I really appreciated this lesson as well as the original poster.

Actually, sodium hydroxide RAISES the pH of the water (done by the water treatment plant presumably). During aging, CO2 from the air reacts with sodium hydroxide, neutralizing sodium hydroxide, leading to a LOWER pH.

When the water sits in the aging barrel, presumably with some agitation or an air stone...or sitting still to the open air, the water will absorb CO2 from the air to establish an equilibrium. NaOH in water will react with CO2 via a number of ways, all ending in neutralization of the NaOH. This will happen even quicker when the water is agitated. When NaOH is neutralized, the tap water's pH will drop to its original pH, which is likely mildly acidic to neutral. Hence, you see a drop in pH in aged, soft tap water if NaOH was added by the water plant. This may provide an explanation for pH drop as reported by the original poster.

This can be demonstrated very easily. If you remember the acid/base titration experiments from grade school (do students still do those??), the solution turns pink or some pretty fuschia color when you reach an alkaline pH. If I remember correctly, they also start with water and either HCl or NaOH. In the case of NaOH, when you add NaOH to the water (plus color indicator), the solution turns pink very quickly. And then by the end of the class (or faster if you swirl it around), the color fades to colorless because your solution's pH has dropped back to near neutral. That is because the NaOH has been neutralized by its reaction with CO2 in the air. The same thing can happen to the tap water where NaOH was added by the water plant. Hope this helps.

[dirtyplants]

Sounds good, but I think you missed your calling.