keeping pH as low as 4.5?

[Marco Lacerda <marcolacerda@ax.apc.org>]

This mail is directed to the guys with experience with blackwater Apisto 
species, like A. paucisquamis, A. elizabethae or A. uaupesi.

Here in Rio the water is soft (4-5 dGH), and slightly acid (pH 6.5).
I'm having problems with the blackwater species, as although blackwater 
Apistos spawn often, on some species 100% of the eggs turn white!!!

I think if I can keep the pH stable at 4.5, I can successfully breed 
these species. I've brought the pH to 4.5 using a mix of fosforic acid, 
chloridric acid, and tanic acid (as suggested by Koslowski, and also by 
Roemer). But this doesn't keep stable for a long time, soon the pH is 
back to 6.0 again.

The employ of peat moss has shown itself not practical, as we're dealing 
with a big number of tanks.

Recently, a German friend suggested some kind of ion-exchange resin that 
can be put in the filter, and keep the water (a soft one, with 4-5 dGH 
like mine) with a very low pH (4-5). It is not a water softener (like 
the ion-exchanger Ca++ for Na+, but something bringing more [H+] into 
the water, hence droping the pH.
Does anybody knows this resin?
Is it available in the U.S.? Where?

All the best, Marco.