i've never heard of "peats" and as far as fish are concerned, neither has Google. Peat moss on the other hand is used in aquariums to modify the water chemistry. peat will soften your water by binding calcium and magnesium ions while simultaneously releasing tannic and gallic acids into the water. These acids then attack the bicarbonates in the water, reducing the water's carbonate hardness and pH.
if that's the "peat" you're talking about, tell us something about your water chemistry and why you think you need peat.