I have a much harder time keeping pH consistent with RO water then with water out of the tap. With 18-20 gallon bubblers, I have to adjust pH down every day. The larger the reservoir, the less it needs to be pHed. This is one of the reasons I went with a large recirculating dwc settup. Complicated to setup, theoretically easy to maintain.

PS. Having grown 2 to 4 plants per 20 gallon containers I will never put more then 2 per 20 gallon container and I will train them away from eachother. DWC has explosive growth. I was given a 4 plant 20 gallon bubbler and it was a dissaster, even after flowering immediatly from clone.