So I ended up with two triple stage filter/carbon and one double di, long story, and I'm wondering if their would be any reason to combine everything into a monster ro/do unit? See attached pictures.
https://www.bulkreefsupply.com/smart-buddie-rodi-booster-pump-aquatic-life.html
I would use the 75gpd ro unit, it's in better condition, get the smart buddie. I see a 5 micron carbon filter and a 1 micron carbon filter. I would change that to double 1 micron, and use the remaining parts to make a 7 stage using 3 di filters using anion, cation and mixed bed resin . The smart buddie is only good for 100 gpd systems. You will get 80 pounds of pressure and your system will be more effective. I get 5 gallons in 40-45 minutes.
I literally just did this last night. I started with a 100G per day BRS 4 stage. I bought a tank and the guy tossed in a heavily used 5 stage. So I ordered the Pro series 7 stage, 200G per day water saver RO and the updated waste valve. Really simple to do. The biggest PITA was packing the 3 DI resin tubes. I had about 700 gallons through my 4 stage and the sediment filter was really dirty, the amount of crap in the bottom of the container was crazy. The 4 stage came 5 micron stuff, this new set up has all 1 micron stuff. It was nice making 150 gallons of water today. Based on how much I made in the time that I did, I can make way more than 200G.
Just look up on BRS's website, they have diagrams that you can follow.