Hi guys , I'm going to be using a 6 pot system 15L pots , 47l res do I need a air stone in the res ? I've read on a few forums that they have effect on the ph ? Is this correct ? Also what would you suggest would be the best growing medium ?I normally use light mix and hand water (very simple), but have read that a base of clay pebbles , along with coco pro has in this system works very well ? I've also seen 50/50 coco perlite I'm no expert so what would you think would be beneficial? Any info would be awsome