I have been running peat in my filters the last 6 months or so on the
recommendation of Roy Hunter and have been happy. The fish seem to like
this condition as do my plants. I don't really have anything scientific
to offer except that I haven't had any problems at all. All my rainbows
are disease free, including 3 Goyders that are about 1 1/2 years old.
Roy can give you more info, I'm sure, as he tells me he is a big
believer in tannic acid. Our water here in New Mexico is quite hard,
about 500 ppm. I also do about 30% a week but have to add RO to bring
the hardness down to around 150 or so.