Have you looked at some of the videos on Bulk Reef Supply about installing and tuning RO/DI systems? 30 psi is too low. Membranes are much more efficient at higher psi. I don't think I've ever seen a membrane that suggest less than 50 psi as minimum pressure. The 30 psi you have right now is not enough pressure to force your source water through the membrane efficiently. That's the reason you're getting so much rejection water. Up the pressure, lower the rejection rate. You need a booster pump and if you're still worried about wasting water add a second membrane.
Reverse Osmosis Accessories