Any reasoning that I can not convert an older RO/DI unit to use GFO/Carbon? I have an older 75gpd BRS 4 stage RO/DI unit that I don't use. Figured replace two of the canisters with carbon/GFO then re-route the plumbing to the two canisters.

Any reason I can't do this?

I also have a few clear canisters that are 20"x4" I could do the same thing.