Peat & Laterite & airstones

About a week ago Stephen Pushak asked if it was the tannic acid in peat
that reduces carbonates and might tea serve a similar function.  I've
heard/read that it is humic acids in peat that lower hardness (calcium &
magnesium hardness much more than carbonate hardness).  Also, I'm pretty
sure that peat would be cheaper to use than tea :-).

Also, Anne Hull Seales mentioned a "glass-bead" type airstone - are these
the blue ones as opposed to the white ones? - for use for CO2.

Also,  I have some peat that I have been using in a bucket to lower the
pH and hardness of my tap water.  I seem to have exhausted the acids a
bit since it doesn't lower pH much anymore but does still lower hardness.
I was thinking of using this "used" peat in combination with laterite as
a substrate for a 25 gal tank.  Does this sound like a good or bad idea?
Should I mix this with gravel?  Any comments would be greatly appreciated.