What kind of water softener do you have? Salt-regenerated ion exchange (the most common type, and if you are buying bags of salt, this is the kind you have).
Yes, it's a salt system.
Such softeners work by exchanging calcium and magnesium ions for sodium ions. Depending on how hard your water is coming in, this may result in quite a lot of sodium in the water (but not the chloride part, so your softener company will half-correctly tell you the salt doesn't go into the water). Regardless, high sodium levels aren't particularly desirable.
Right, from what I've read, it's not ideal. As I understand it, the softener is replacing calcium and magnesium ions (not free floating, but bonded with something? this is where my lack of science background shows) with sodium ions, so it's not making salt water, but it is increasing the sodium content and taking away beneficial calcium and magnesium. I assume that the RO process that happens next (for my kitchen tap) removes the sodium issue? So maybe that's the fix for that issue, although it leaves me with an annoying water change process. Anyone that does RO, let me know if there's a way to do this more quickly than getting it from the slow tap that's typical of RO house systems. We're getting our water system serviced this week, so maybe I can ask the guy if there's a solution for that (maybe a second line from the RO tank that I can pump to the aquarium? out of my depth here).
This process also should have no affect at all on the KH of your water, so the fact that the KH it is really low seems odd.
That's what I thought too; not sure what's going on there.
I'd also try letting your tap water sit out for a while and re-test the pH... Sometimes tap water is heavily depleted of CO2, and that temporarily raises the pH.. on exposure to air for a few hours it goes down.
In process. I left some out this morning, so I'll check when I get home (will have high pH kit by then). I also put the water into my tank and let it sit overnight. Still high pH this morning. FYI, no fish or plants in there -- just a piece of driftwood and floramax capped with sand. (The driftwood appears relatively inert so far, not seeing any tannins yet, though maybe it's a slower process, and I haven't set up my filter yet, so water flow is nil).
If I go with RO water, it looks like Seachem Replenish may be the first step, and then a combo of Acid Buffer and Alkaline Buffer to achieve desired kH/pH balance?
I'm not super concerned about getting an exact pH -- more concerned with stability -- but a decent kH buffer and a pH in the 6.5 to 7.5 range seems like a reasonable goal.