Capn Style Grow - Airstones?

Hello everyone,
I've been doing a ton of research for my first grow and came across the capn style of growing explained here.
http://dudegrows.com/doing-it-captain-style-part-2/

My question is why do the individual reservoir not need air stones? With the pumps only running twice a day for 15 minute intervals I'm curious how the water doesn't become stagnant. Is it because of the beneficial bacteria (recharge) hes using? Don't get me wrong, i'm happy to not have to place a stone but just curious as to the reason why.

Thanks!

Anyone?

The reservoir do have individual air stones thats the yellow halo thing. Water quickly looses any oxygen stored in it if there isn't an air stone running. Easier to stick with good quality soil and PH the water correctly take it easy with the nutes and give them plenty of light and the weed should flourish m8