[Myka]

What type of flow restrictor does it have? I haven't seen one with an adjustment. Got a pic? I couldn't even find anything with Google.

Have you tried removing all the filters and run the system empty to check for clogged lines? Or you can remove each line one by one and blow through it. If you have new pre-filters and the lines aren't clogged then it has to be the membrane.

Fwiw, you shouldn't have more than 100 psi going into the system as the fittings and housings are only rated to 100 psi. It sounds like you don't need the booster pump at all. What is the psi without the booster?

I have a 150 gpd RO membrane in my system and I've tested it with and without a booster. With the booster I get 85 psi and without the booster I get 62 psi. I use a 75 gpd restrictor with it which slows down the waste water, and I get exactly 1:1.7 either way. I get 130 gpd product water with the booster and 110 gpd without the booster. So I've decided there's no point in my using the booster. The membrane is 5 years old and it's made quite a lot of water, plus I use the slower restrictor so it isn't flush as much as it should (I have a manual flush on it), so that's why it's not running at the full 150 gpd.