I am not new to paintball, but I don't know much about hpa. I have a spyder pilot acs and am considering buying an hpa tank. My question is what mods if any will I need to run hpa, and can I switch back and forth between hpa and co2 without causing problems. I ask this because I play at two fields and only 1 fills hpa. Any quick help would be greatly apreciated. Thanks.