Re: [Killietalk] Deionized water - PH

[Wright Huntley <whuntley at verizon_net>]

luiz rulff wrote:
> Hi, fellow killinuts.
>
> I got good deal on a deionized tap water filter.
>
> My tap water is very hard, sometimes TDS around 580 ,,,, with this filter the output water has a TDS 06 ,,,,, very good ,,,, but PH 9.8.
>
> How can I safely change PH to 6.4 without increasing the TDS.
>
> I tried the acid buffer ,,,,, PH changed OK but TDS increased to 220.
>
> Thank you all.
>
> Luiz
>   
Luiz,

To understand the pH of very pure water, you must learn about buffers. 
They are the mixture of a salt and its weak acid (or base).

The amount of dissolved salt and acid determines the equilibrium between 
salt and acid, so sets the pH at some value. Adding acid causes very 
small change until the salt has all been converted to another form, and 
the pH suddenly starts to drop. A common buffer in US tap water is 
calcium (and magnesium?) bicarbonate (from underground limestone 
deposits). Dissolved atmospheric CO2 causes carbonic acid to form the 
buffer system.

Distilled, RO and other pure water have essentially no buffering, so the 
pH can be really wild. It will swing with tiny traces of acid or base, 
but is basically meaningless. You must raise the tds by adding a salt to 
buffer the pH and make it more stable. Baking soda (sodium bicarbonate) 
is best as a little sets pH in the high 7s, which is a chemically safe 
region.

Fish and plants can't feel or react to pH except at extreme values 
(below 4 and above 10, IME). Some reactions, like conversion of harmless 
ammonium to toxic ammonia, do depend on pH so the fish can be poisoned 
by the ammonia at higher pH (above 8, usually). It is not the pH, but 
the ammonia that kills.

I would bet that your RO-water pH would drop dramatically if you just 
aerate it for an hour or so. CO2 from the atmosphere will cause a "pH 
crash" in the absence of any buffer system. Nitrites can be deadly at 
lower pH (brown-blood disease), but a little table salt is protective 
for that (again raising tds in the process).

I regard a tds of 80-100 ppm ideal for soft-water species. I never use 
water much below tds 50 for anything but hatching difficult eggs. It is 
virtually poisonous to most living creatures, because it is not buffered 
well, and allows wild chemical reactions to happen in very unpredictable 
ways. Your RO water is great for tempering your tap water, but not 
suited for most fish, IMHO. Without at least a little tap water, your 
fish depend on food alone for all the essential trace minerals, and food 
is rarely sufficient.

Wright

-- 
Wright Huntley - Rt. 001 Box K36, Bishop CA 93514 - whuntley at verizon_net  760 937-2276 (cell) 760 872-3995.

My VCR just blinks "12:00" all the time.  I wonder if it will update
itself to blink "12:00" properly when the time changes.

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