Straight RO water for the flush? And since I also use hydroponic nutes for my grow how should I go for the ph level I usually start at 5.7 for veg and in flower I start raising it slowly
I don't like ro water for potting mix much. No alkalinity in it. It actually would be better for leaching with a low dose of nutes in it.
Professionals in food production test their source water and if too hard mix down to 150-200ppm by combining with ro.
Or they add acid like ph down but to nuetralize too much calcium carbonate. No need with ro water.
I would use tap water if I knew what was in it. If I had to use ro I would mix it with tap or add maybe 15% nutes. Salts are attracted to salts.
For your yellowing question below I like to keep them green to the end by tapering my nute concentration down as they ripen. And never overfed during the cycle for best results.
I add fertilizer at a low dose every watering once needed when the soil depletes of nutrients.
Plants also don't need any of the bottles you are using except a complete veg nute. The bloom nutes are not needed. It's a myth to sell more bottles.
Better to learn on a 1 part balanced Grow nute. 1 bottle simplifies things. Additives are only needed to cure specific deficiencies. And even then a base fertilizer usually takes care of it.
Hope this helped.