Yep, that's what I've used it for before and it seems to help.
As for considerations... It does contain many small particles that will cloud the water if not careful. I usually make a small pouch out of some filter floss material and wrap it up good, then stick it in my filter somewhere so the water goes thru it. Of course, the amount of peat you will need depends on several factors... aquaium size, water properties, and ultimate goal.
Best bet is to start small and work your way up using accurate test measurements as a guide. Don't rely on just looking at the water for color changes, sometimes it will change, sometimes it won't!
Also, keep on eye on the fish and see if you notice any behavorial differences.
Also, if you are using CO2, be particularly careful as the ph level is effected more the softer the water.
Good luck,