Thanks for thatAS your beer is already partially carbonated, try 40PSI and shake the keg for a few minutes. Reduce to 30PSI and leave for about 5 hours. Reduce to serving pressure and an hour or so, pour a beer. If still not enough carb, raise pressure to 30PSI for a few more hours. You will soon get the hang of it. There are online tools for calculating "set and forget" carbonation settings but these are not much use if your beer is already partially carbonated and you want to quickly do a forced carb.