You certainly have enough hens to justify at least one more rooster if you are wanting fertile eggs! I successfully maintain 1 rooster for every 6-8 hens in a coop and have not had any problems. My coops all have between 20-30 hens plus appropriate # of roosters. I never introduce a lone bird, rather, introduce at least 2-3 at a time, and bring the newbie in at night while everyone is on the roost. They seem to adjust to a new bird better if they wake up in the morning to find it there rather than introducing it during the day.