Keg Leak or Carbonation?

I'm going to keg for the first time soon (hopefully tonight) and in preparation I replaced the o-rings around the dip tubes and thoroughly cleaned the keg. I then filled it about 2.5 gallons of starsan and sealed it up. Today I decided to make sure the keg was holding pressure before I put all the beer in it, so I pressurized it to 20 psi and then turned off the gas. When I came back a couple hours later, the pressure was down to 18ish. At first I thought I had a small leak somewhere, but after going over everything a few times I suddenly realized that it might be carbonating the sanitizer.

Any thoughts? Would the psi drop be that quick? The keg is at room temp. Should I drain the keg before I try to figure out if it's holding pressure so that carbonation doesn't come into play, or does it not matter?

Thanks!

Sounds normal. The co2 saturates the water when under pressure like that and will eventually find an equilibrium. You can always check for leaks with a spray bottle of soapy water, but you should be fine.

Yeah I've sprayed around everywhere I can see, so unless it's leaking from the QD then I should be fine I suppose! I just wasn't sure how quickly the sanitizer would absorb the CO2, but I'm glad I stopped to think about it before I went crazy trying to find the leak!

Thanks