Perhaps you can adjust the membrane pressure by partially closing a valve on the reject line. Close it until you reach the desired 150 psi. If you don't have a valve there you could add one.
Normally you would increase the pressure by reducing the reject. I doubt your system recirculates any of the reject, so you'll want to keep the reject/product ratio at least 2:1. I believe factory settings call for 3:1. The pump could be going bad, or someone may have replaced it with the type that has an internal pop-off that needs to be adjusted up.
Any suggestions on how to get the old filter out of the PVC membrane? It seems to be quite stuck! I've ordered a stainless one in case I can't get it out, but would like to save it if possible.
Yes, remove the retainer from one end, then using a piece of wood and a hammer drive the membrane and end caps through. You can sometimes "bump" the system on and let the pressure push the cap out, but it's not a very safe way to do it and if the membrane is stuck it won't help at all.
Some have a big C-clip, some have pins. With the C-clip, you only need to remove one on one end and drive the whole thing out that way. With the pins you need to remove them on both ends so both caps will slide.
This is different than what you asked but here's for what it is worth.
I changed brands of membrane once & found out the hard way that the new membrane works & was the right size but required an adaptor fitting. My membrane is the chlorine tolerant CA type so it is not nearly as common as the one that requires the charcoal filter.
Thanks for all the great info and help. Got the new filter in and it's producing great spot free water. Noticed that the discharge water seems to be far less. In fact, it appears that it is even less than what's going into the tank. Is this normal after changing a filter??
Did you check the tds? I saw the oppisite when I changed my membrane out. If the tds is good, then I wouldn't worry about it. That would be my first step though.
You shouldn't have more product than reject. That leads to a clogged membrane. Systems are different, but they should never discharge less than 1:1 with the product. You may just need to open a valve to increase the reject flow. If it recirculates part of the reject back to the pump it should be 1:1, but if no reject is recirculated it shouldn't be less than 2:1 reject to product.