Just to be clear, RO or ion exchange can both be done at the whole house level when the water supply enters the foundation or you could do RO specifically at a point location (like kitchen sink). I don't think you can do ion exchange at a point location. Due to the buildup of radioactivity, I decided early on I was only going to do a whole house solution. RO uses water to clean water and because I am on a low flowing well and I am on septic, wasting water for the RO and then having the wasted water run out to my septic wasn't going to be an option I considered so RO was immediately out leaving me with only ion exchange. That was my thought process but there are certainly reasons why you may come to a different answer.
I went back and looked - I initially tested for gross alpha and radon (they were both cheap to include). Gross alpha came back 41 piC/l (radon was 1500 piC/l) so I decided to test for uranium because it was cheaper than radium and uranium came back 12 piC/l. There was some sort of math adjusted gross alpha calculator too that the testing agency provided to justify not doing anything for the uranium. But I wanted none of that because the gross alpha was still way too high, clearly some was coming from uranium and likely the rest from radium. because of my low level of radon, i felt I could treat that with carbon but your air tank is a much preferred way of doing that and I would stick with it if you already have it.
Yes, 1 bin full of salt and both the cation and anion exchange tanks draw from the same bin
So I have three tanks that backwash - cation, anion, and carbon. I put a standpipe into my house's DWV system and the three tanks run into this plumbing manifold thing I created that then runs to the standpipe with an air gap so it all gets routed to the septic. I had a thread on here about it - maybe if you search my user name for posts you can find it.
In theory, calcite should bring the water to neutral and then stop but in practice I'm not sure it works that way. I didn't go the calcite tank direction because I didn't want to add back hardness to raise pH after I had just removed it (along with the radium). I like what I got with the soda ash injection. you might be fine without either since you are starting out near pH of 8 and not need any pH adjustment. If I was in your shoes, I might skip it, see how the system works, get a pH meter and test the water at faucets to monitor. If you have pex or cpvc, don't even bother. If you have copper, I would monitor pH to see what if anything needs to be done.
I have found that interior fluctuations in pH are more related to the incoming water pH fluctuation than anything else (at least once the system is over the "new" phase and soda ash injection amount worked out).
You want to feed the anion with soft water so do softener and then anion. Not sure if it matters on the radon air system other than if the air system is also oxidizing anything else (unintentionally like say iron). So it might make sense to have the radon air first bleeding off radon/oxidizing stuff you don't know is there before running through the softener. I would also consider a carbon tank after the anion. I have never run the anion alone but there is anecdotal evidence that anion can mess with water smell, taste, color which is what the carbon is perfect at fixing. Plus carbon cleans up pretty much any other thing dissolved in water that the two ion exchanges don't take care of. I know, its starting to get crazy but this is what happens when you have to be your own water treatment plant. Frankly, I would rather have me in charge of what I am drinking than some bureaucrat (ie Flint, Newark).
you are apparently already dealing with radon, now you found uranium and my guess is you probably have a radium issue too. Off hand I can't remember, but one of those (radium or uranium) was expensive to test for. So I tested for gross alpha, then the less expensive of the radium or uranium, and then whatever gross alpha isn't being fed by what you tested, the other one is the likely component. Lucky me wound up with nearly 50% gross alpha from radium and 50% gross alpha from uranium. (with some elevated radon, yea!) Your options for uranium are RO or ion exchange. I choose ion exchange for the reasons I list in that thread.
