If you have whole house salt water filter/ water softener you should instal a whole house canister filter, which you can instal a carbon block, or particle/micron (cotton) Whichever you want, after the softener. Like this
https://www.doityourself.com/forum/...nt-image-ee48afa6d3750da1f96b323f19ad17a7.jpg A softener is basically like a chemical magnet. Depending on what contaminants are in your water, doesn't necessarily make the water cleaner, just softer. Typically, with well water, a whole house canister filter gets install after the softener. Sometimes, if the water supply is dirty enough, you put a big micron, like 10, before the softener, and another canister after the softener, with a smaller micron, like 5,1, or a carbon block to polish the water and remove any resins the softening might be adding.
Take a sample of your tap water to a pool place and have em test it for chlorine. Pretty sure the salt removes all the chlorine.
The way an ro/di is plumbed is...
Micron (cotton), then carbon, then membrane, then resin= product water ready for tank. Like this
https://blog.marinedepot.com/wp-content/uploads/2017/02/rodi4.jpg Resin is expensive and is only supposed to take out the remaining few tds. The membrane will take out 95%, and the micron/particle/cotton take out whatever they can, depending on size of your contaminates, before the membrane to keep it as clean as possible to make it last. Carbon block protects the membrane from chlorides and fluorides because they will harden the membrane right quick and turn it to useless.
Some people double up stages. Like 2 carbon, 2 micron, whatever. In your case I would run 2 dif size microns, not 2 membranes. And would suspect if you did want to run 2 membranes instead of two microns, the membrane first inline would get used up quick, and the second would need a booster pump because the pressure would be too low after the first membrane.
If your tap water is 700s after whole house salt/softener, def add a canister filter after the softener for the whole house
