In my experience with infrared films using a Hoya R72 filter, I always meter the visible light and focus, apply the filter, adjust to IR focusing marked on the lens and adjust / bracket +4 to 6 stops. Never had a problem with any infrared film and the results are amazing! As far as ASA/ISO goes, I either follow the retailer's suggestion or set it at 200. I heard with these new IR films in the market today, a Red 25 filter is impracticable but I have never tried it for myself. I am a big fan of EFKE IR820 Aura because it's the closet film to Kodak HIE (R.I.P.).