What up Olds - You should take midgrade's advice on this one - at LEAST one airstone per bucket. I'd say, even with my limited experience, that one 6" airstone in a 5gal bucket is not nearly enough. And yeah, Petsmart's got a nice selection of airstones, but their pumps seem to be way overpriced. I was going to buy my airpump there, but ended up finding it quite a bit cheaper at good old walmart. I'm using a "Whisper" air pump - by Tetra, I think - rated for 30-60 gallons, with dual outlets, in a 6-8 gallon res. My plants seem to love it, and it was pretty cheap. I have to admit, I have no experience with other air pumps, but in case it's relevant, this one definitely does NOT whisper! Depending on how close together your buckets are, and if money/space/electrical outlets are an issue, you could buy 2 decent powered ones with multiple outlets, and split them off. Not sure what would be more of a hassle: having 5 separate small pumps, or 2 larger ones with a tangle of airhose and splitters, etc.... I'd wait to hear from someone experienced, and familiar with your type of setup. Good luck man, Peace