This is the first time I have kegged my beer. After putting gas lines on my kegs I turned the pressure up to 10 psi. Checked the gauge ab 2 hours later and gauge reads 20 psi. I unhook the gas line, release pressure from kegs, set regulator back at 0 and reconnect and turn up the regulator to find pressure at 15 psi 30 minutes later. Temp is at a steady 40 degrees and CO2 tank is in the keezer. What is going on?