here's the scoop on peat that i will use some internet info to help me explain. many people like to run peat in their filters, but the best way to do it is to age water with peat, then add it to your fish tank during water changes instead of using tap water.
good things about peat: it lowers the Gh (calcium and magnesium content) and Ph when soaked in water for a set period of time.
bad things: it is expensive, cheap peat at garden supply stores often contains harmful chemicals, it turns your water a urine like color (some like this)
bad things about running it in filters: it clogs easily, it is hard to determine the amount of peat you need to keep your water chemistry the same after water changes, some peat is less effective than others, it doesnt do anything to your kh (carbonate content), so your ph will go right back up once the peat becomes ineffective or if you dont add enough during water changes.
bottom line, it really isnt worth the money, time, hassle, urine water IMO.
M