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Re: PH Drop

> Date: Sun, 1 Sep 2002 01:05:29 -0500
> From: "Steven Maier" <stevemaier at ameritech_net>
> Subject: PH Drop
> Most likely causes for PH drop. 1. New CO2 ( Was using a tank that had been
> unused for perhaps one to two years and just got it refilled ) 2. Removed
> large mat of Glossostigma and possibly released some Hydrogen Sulfide.
> Any other ideas? Normaly with regular weekly water changes I can maintain
> the PH at 6.5 . Over the past few days I have been shutting the CO2 down
> quite a bit to maintain the ph above 6.3 . What are some reasons that PH
> drops? Plant growth and algae growth are both very acceptable.
> Thanks
> Steve

The most common cause is that the acid buffers are used up by the addition 
of weak acids, either CO2 or fish/food-produced (or maybe your H2S).

Many water system have drastic changes in hardness, tds, and alkalinity as 
summer demand makes extra loads. They get water from new sources that are 
different from winter water. Therefore, the KH often can be lower, 
sometimes overnight.

Our Modesto water dropped from about 300 ppm average tds (100 ppm CaCO3 
equiv., KH about 6 degrees) to about 30 ppm! That is less than 2 degrees 
on GH or KH no matter how you look at it! In practice, Sierra snow runoff 
water never sees anything but inert granite (no limestone), so the KH is 
essentially zero. pH is only high, initially, because they add NaOH or CaO 
to prevent the water from etching lead out of pipe joints. Neither are 
parts of effective buffer systems, AFAIK (at least until the CaO is 
gradually dissolved by some water and atmospheric CO2 to form CaHCO3).

Never try to regulate CO2 by pH alone. A fresh reading of KH is mandatory, 
in summer, for the chart to be reasonably useful. If you start with really 
low alkalinity (formerly called "Carbonate Hardness") it can be quickly 
used up by the plants themselves, and pH will "crash." Add good Ca and Mg 
HCO3 buffers to get a KH of 4 or more plus the essential minerals Ca and 
Mg (hence, GH of 3 or 4, too). I think there are RO correction additives 
and/or Rift Lake salts that can fix it with $$$. Cheaper oyster grit or 
crushed coral in filter chambers probably can do it, too. All may be a bit 
slow, as the good stuff is only very weakly soluble in higher pH water. 
Steve Dixon is our local resident expert on how to deal with this problem, 
as SF gets the low KH water all the time.

Since my water has very suddenly turned into water like his, I hope Steve 
D. can chime in with some help on easy ways to stabilize KH at the right 


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