If you are doing regular water changes the chem additions would not be necessary depending on the calcerous animal load in the tank.
To best determine the amount and frequency of any addition you should first "map" the rate of depletion for a few weeks or so. It will not be the exact same from week to week but will give you an indication of what the tank uses and needs.
In in large tanks and/or higher use systems, ionic two parts solutions will not really fill the need. If smaller then daily additions in equal parts should work providing the chemistry is balanced at the start. For more demanding systems you can use kalk
(to maintain only), dry buffer and CaCl
or possibley a reactor.