Russ will probably ask if your water is treated with chloramines or not.
Check w your local water company if you are not sure before you call.
Whatever system you end up with, try to stay with carbon blocks 1 micron or less. They last much much longer than a five micron block.
Bulk Reef...
I would suggest getting one from either Buckeye Hydro or Spectrapure. While they are not made to neatly fit under your sink, they do what they are made to do. And, the sediment filters and carbon blocks are universal and can be purchased numerous aces, both locally and online. Both companies...
I can tell you from years of keeping saltwater fish, the biggest issue with RO membranes is TDS creep.
Click on the description to get a better explanation than I can give.
https://www.buckeyehydro.com/tds-creep-bypass/
The initial water coming out of your membrane is often HIGHER in TDS than...