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Re: V3 #499 and Low pH problem

Like Jim Capelle, I received only the beginning of this morning's 

The APD archive contains two letters regarding use of alum and/or pyrite 
to lower pH.  I don't know of any accepted method for using either of these 
for controlled reduction of pH.

If I were to experiment with either one then I might experiment with alum.  
You can get it in the grocery store where it's usually stocked with the 
spices.  When mixed with water alum should precipitate aluminum hydroxide 
and leave potassium sulfate and sulfuric acid in solution.  The acid will 
attack bicarbonate in the water and lower the water's buffer capacity and 
pH.  The precipitating aluminum hydroxide may also remove phosphate from 

Between dropping pH, reducing buffer capacity, adding potassium and
removing phosphate it seems that some people could see several gains from
treating water with alum.  On the down side, I expect this will be a
pretty expensive way to do anything. 

I HAVE NOT tried this.  As always, experiment outside any aquarium and 
apply it to an aquarium only with great care.

I wouldn't experiment with pyrite.  If pyrite oxidation caused the low pH
problem that started this thread, then it did so only because of that
gentleman's low buffer capacity.  Pyrite oxidation under water is normally
biologically remediated and without the right bacteria it probably won't
work.  Probably the only way to get it to work at a rate high enough to
make a significant difference in well-buffered water would be to powder
the pyrite and to use it in fairly large quantities.  Under those
conditions the rate of the reaction would be unpredictable. 

The reaction probably would proceed in two different stages.  The initial
reaction happens in the solid state and probably will release sulfuric
acid and produce soluble ferrous sulfate.  Under water the ferrous sulfate
can leach out of the original site before the iron is oxidized and
precipitated, probably as the oxyhydroxide.  That could put iron stains on
other ornaments in the tank, but it would also have the side effect of
pulling phosphate out of the water. 

Again, I haven't done this, I don't advise it, and I wouldn't even want 
to experiment with it.

If you have heavily buffered water and need to lower your pH then there is
only one means I can actually advise you to use.  Mix your water supply
with RO or distilled water to reduce the alkalinity.  Afterwords, lower
the pH with CO2 additions and increase the pH with aeration and water

Roger Miller