ro/di

Yeah... Just south in CV we hit about 750 out of the tap. After membrane its usually about 6 and di clears it up. I run a dual DI system, keeps DI cost down and safety up!

I flush before I make a batch of Water change water. but not much after that, my system tops off through the RO unit, so its always running. As far as filter changes go, I usually know that when the first filter is red enough, or a magnet can stick to the side of the cartridge sump, then its time to go. Carbons usually get changed then anyway, but before that I would go on a 15+ PSI drop then change carbon.
I've had this particular unit.... 2 years...maybe 3 and have yet to change the membrane. I would certainly NOT flush bleach into my system or through my membrane at any point for any reason. but that's just me.