I use it both ways that Somonas outlined, for the discus/rams, and the Angelfish/apistos/little discus.
I use filter baggies as knee-highs disintegrate/rot after a couple of months.
I use the granulated peat (Fluval) IN the filters, and garden peat moss (nothing else added, 100% peat) in baggies in buckets for changewater.
Water out of the tap is pH 7.8 KH5 GH11, after 24 hours in the buckets pH6.4 KH2/3 and GH 10/11.
Tanks with the peat in the filter WITH altered changewater pH 6.8 KH 4
Tanks with peat in the filter, changewater straight from tap pH 7.2 KH4
I COULD use more peat in the filters, but I know just what to expect with what I have going on now, and wouldn't want to crash the system by fiddling too much.