Warren
I have two 300gpd RO Man units and one 4 x 40 commercial unit.
The two 300gpd units are running nearly constantly to keep up with our workload, they are both pumped and we are getting a water pressure going in of 100psi - just on the red.
One unit has been running for 2 years the other one for 1 year. I have never changed any filters and do not use polishing resin. We are getting a 000 purity level.
I believe that not only do you need to have a booster pump but the extra pressure could make it possible to not use resin.
I think that resin is a ploy from the suppliers and something that is not required - if you can get a decent amount of pressure.
In six months we have used 124000 litres of water and I am still getting 000.
Rob