Adding more fish to quarantine tank

[AdamsB]

For a little over a week I've had a ~3" yellow tang in quarantine in a 20G long. I'd like to get a few green chromis, 2-5 depending on what the lfs has. Could I add this many to a 20g? I've been doing 25% water changes twice a week so far an feeding lightly twice a day to reduce waste. No filter just air pump and power head, I plan to add some spare live rock from my sump today to eliminate any ammonia that may start to build up. I'm not dosing any meds as of 6 days ago.