Lapis Lustre and Chem/pH Qs

I've used Lapis Lustre in a 140 gal tnak for a while and have not 
noticed any problems, although I suppose they may not yet be 
apparent.  I tested a sample of it with muriatic acid (don't inhale!) 
and there was no significant bubbling.  Maybe we're talking about 
different varieties of this sand/gravel.

I need a recommendation abotu how to change the pH in my tank and 
buffer it safely.  The tap water is over 8, and I'd like 6.5-7.  I 
used Acidifier to lower it at first, but it bounced back quickly and 
then I read the bottle and found that it was Sodium MonoPHOSPHATE 
(argh).  Anyway, I can get almost any chemical imaginable- I just 
need to know a safe recipe for changing the pH and buffering it that 
won't harm the fish or help out the algae (a CO2 system is in the 
works- but it will be a while before I can change the pH that way).

Nick Livingston in dreary Seattle, using a new mail reader that 
hopefully won't have wretched little "="s everywhere.