I've had many spawns that were spawned and grown out in pretty hard water, 400+ TDS. Never had to use RO with rams. Just be very careful cleaning the tank. Ram fry are very small and scatter all over the place for the first week and it's easy to suck them out without knowing it. I do bare minimum cleanings during this time.
I feed them Hikari First Bites for the first 3 or 4 days because they're so small and just started a 4 day old batch on BBS this evening.