I recently kegged my first batch after a whole lot of research. I brewed a Cream Ale (BJCP guidelines suggest 2.6 volumes CO2). After racking it from the secondary to the keg and purging three times at 3-5 psig, i relieved the pressure to about 2 psig and let it cool down to serving temp (about 48F). Per my handy force carbonation chart, I needed the keg contents to come to equilibrium with 18 psig at that temperature to achieve my target carbonation. I set the regulator to 20 psig and rocked the keg for about 10 minutes. It was still taking gas, but I didn't want to overdo it so I dialed it down to 18 psig and continued rocking for a few more minutes until it stopped taking gas. I let it sit overnight at 18 psig, then adjusted to about 12 psig for serving. It has been all foam, even a week later. Since then I have purged the head space down to 3-5 psig and rocked the keg to try to get some of the CO2 out of solution. When I do this, the pressure doesn't ever rise and I don't seem to be releasing any more gas. My question is this: how do I lower the carbonation level?