I'd go for an air-stone as well. If the ammonia is converted to nitrate (NO3) (and it will be eventually, even without the air-stone) you don't then want anaerobic denitrification (NO3 ~ N2 gas) to occur. If the the oxygen levels are higher it will just remain as NO3 until the plants use it.
See @Kalum I'm not as daft as I look....I couldn't possibly be Wasn't a bad guess. Told you they'd be here as soon as they finished work, they can't resist a good bacteria discussion