Hey bro, no I haven't been using an airstone in my res last couple grows (not that I don't recommend one). If I'm away for an extended period I do put a pump in there to help keep it mixed and last longer (
This pump works great and can run dry without damage). Normally I pretty much never fill up my res completely though since I try to make it last just enough for 5-6 days... The res will stay good and pH stable for at least a week but going much longer than that can cause problems including clogging up the aquavalves.