The answers below are ...

The answers below are technically correct, and , in fact, most resin manufacturers now offer software for this function, but there is one additional consideration. Traditionally to somewhat standardize the mechanical design of the vessel and laterals, the standard ratio of cation to anion exchange resin is generally 1:1 or 2:3, depending on the breakthrough point you want. In the 1:1 you should break on silica, whereas the latter will generally break on conductivity.