Nope. Just do what most people do try and work with the water coming out of your tap. If doing continuous changes, use tap water with a pre-filter and Dechlor (or equivalent) de-chlorination cartridge.are there any other systemic solutions that would make sense?
A lot of discus keepers just use tap water with a HMA filter.
Nope as well. Switching to potassium chloride would be OK, but as stated about 5 times the cost.can I install some additional filter at the exit to remove the Na ions?
You could of course use RO water, possibly mixed with tap water if you really insist on having carefully controlled water.