Thanks guys, the reason I settled on 5 ppm is because I use to get my RO water from Wally world from one of those machines. The water tested at 30 ppm and after a few weeks ended up burning most of my Neps. When I flushed the pots the water flushing out from the bottom of the pots was reading 200+ ppm. I'd rather spend the 30 bucks every 5-6 months than do a periodic flush and watch each and every pot.
The RO water pre-bottled from wally world was reading 7-8 ppm back from I purchased it so I figure going with 5, maybe even 10 ppm is a safe bet.
The only other option I can think is that the machine wasnt filtering out something that caused the plants to decline.