Dramatic change in tap pH

cut n' pasted from www.skepticalaquarist.com:

"The quicklime (calcium oxide— CaO) used in this "lime-soda" technique is produced in a kiln, where heat drives the CO2 out of crushed coral, limestone or oystershell. The resulting caustic quicklime can be finely ground and slaked with water to form hydrated lime or calcium hydroxide (Ca(OH)2), a fine powdery alkali that is strong enough to neutralize powerful acids. The slaked lime is also an efficient absorber of carbon dioxide, so tapwater treated by "lime-soda" softening generally arrives at the household tap still depleted in CO2, which contributes to its high pH. Often fishkeepers with this artificially softened water that is combined with high pH find that the pH drops somewhat after 24 hours of curing, aerating it in a water butt. For the sake of pH stability in the aquarium, lime-soda softened water should always be separately cured before using it.

In areas with soft, naturally acidic water, utilities sometimes boost the pH, to reduce corrosion in the mains, by adding calcium hydroxide alone. This can give tapwater with unusually high pH. On the whole, if tapwater has a pH >8.3 or so, you should expect that the water has been "limed."'
 
bingo

You know WetmanNY, I found that very quotation on your site when reading about live foods and more just today. Good site. Hmmm, maybe I should spend some more time there....

Yes, you were correct about what our water company is doing to the water. Since you or someone elsewhere said something about Potassium Chloride lowering pH, (I have been reading a lot of archives and sites today) and KCl (NuSalt) being one of my ferts, maybe I could just fill a bucket, add some KCl and stir, and presto! have suitable angelfish water!

Right?

If my tank pH is 6.8 +/-, and I change 30% of the water, the highest pH of my new water should be ? to keep tank pH under 7.0? My guess is somewhere around 7.2, but if anyone can do this log math, I would appreciate it.
 
um, OK. Thanks!

Could you briefly run through some of the logic for me? I thought that since it was a logarithmic scale it would be more than just averaging as in 70% x 6.8 + 30% x X = 7.0 If I plug in your 7.96, I would get 7.15 (more of a change than I want), so I presume that my method is indeed faulty. So how you came up with 7.96 is a bit of a mystery to me.

Not stupid, just ignorant.
 
.7 * 10 ^ -6.8 + .3 * 10 ^ -pH = 10 ^ -7.0

I kinda did it bass-ackwards, but wound up with the second number. I'll have my roomie confirm, and then send you a complete formula.
 
Upon further review, there is no way to do this problem without taking equilibrium constants and hardness taken into account. It would be a hell of a lot harder than that which anyone in my dorm could do in a "reasonable" (read: less than an all-nighter) amount of time without software doing most of it for us. We don't have the software, so empirical experimentation on your part might have to suffice.

Both times, I went for too simplistic of a model, so do not take those numbers as Gospel, or even a failed attempt at Scripture.
 
Under the assumption that you have water mixed with NaOH in your tap and water mixed with HCl in your tank (and no buffering), 7.41 is the max. However, your buffers will help increase this value...by how much? We may not know without empirical experimentation.
 
Hi! I owe a couple of apologies here - one to WetMan, for doubting him (the man who accepted my iodide calculations without question - shame on me, bring out the wet noodles, or string algae, whatever) All that time, and I didn't know what county water was doing. I was working with city water, and it's probably the same, just noone ever explained it. In my defense, my super also believed the residual ammonia caused the transient high pH. So sorry, WetMan, I'll read your book more closely before I open my mouth and put both feet in (yes, they fit)

Matthew - post any more of those calculations, amd I'll have you banned - I flunked that part of quant :)

Tom - how would you feel about having some pH paper that's a lot cheaper than whatever you're using to check ph?
PM me.
judy
 
Apparently, I would flunk that part of quant, too, Judy, as my roommate had to explain to me what happens differently around the pH that we simply call "neutral" (head exploding, sprinting to an exit!!!)

No more pH calcs for me...don't ban me, please? I'm a good kid! :D

(I took your last statement with a grain of salt, 'cos I wouldn't want you thinking that I took it seriously this time!!!)

~Matthew
 
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