if we can believe what we have been told so far on our reverse osmosis (RO) journey the total hardness (Ca++ and Mg++) of the water output from the RO unit will be in the region of 8-12mg/L (ppm if you prefer)
then we add on the re-mineralisation filter which has stated Ca++ and Mg++ values of 34mg/L & 12mg/L respectively for a total hardness uplift of 46mg/L
while i enjoyed chemistry at school i can not recall if it is valid to add the TH hardness of the RO output to the TH of the remineralisation cartridge, but if we assumed 10mg/L TH output plus an additional 46mg/L of TH from the remineralisation filter that would theoretically give us a TH of 56mg/L, which would be pretty much ideal
anyway, next week the RO unit will arrive and we can connect it up and run some empirical testing and there will be no need to theorise further. lets see. it will be fun, whatever happens
in the meantime, here is a link that might be of interest;
http://www.mineralwaters.org/index.php/index.php?func=f&parval=content/hard