i have been growing w a flood and drain for many years.. 4x4x4inch rock wool medium..my veg is a 2x4ft table w a 30 gallon rez,, my bloom is a 4x6ft table with a 50 gallon rez....the pumps flood the tables for 15 minutes once every 6 hours, lights come on at 5pm off at 5 am in my bloom, veg on at 5pm off at 11am pump timers set to flood at 6pm, 12am, 6am, 12pm...
i use to have air pumps w/ air stones in the rez that ran constantly keeping water very oxegenated.. now i just have the flood n drain pumps no air stones because as soon as the pumps go on to flood the table, the water fall of run off airates the hell out of the rez.... i have never had problems w rez water,, yes it sits 6 hours at a time but the flooding and draining keep the rez oxegenated enough so that i dont feel the need for air stones or anything,,, i have a drain at the bottom of each rez tote,, so changing and cleaning is simple.. every 2 weeks i drain, fill w water and nutes, then turn on the pump for a few minutes to mix it all up.. then i top off the rez every 2 or 3 days w/ plain ph balanced water till the next rez change... my plants are happy n healthy no need for air stones in a flood and drain set up,,as the flooding and draining do all the airation u need