They way you determine how much you need is by monitoring your levels between water changes (pH, Cal) with frags you shouldn't need much. Once you have determined how much your tank is consuming you can set up a drip method that adds close to the same amount that is being consumed. If your Cal is going from say 400 down to 350 and then with a water change goes back to 400, you probably don't need to start dosing yet. But if you Ca
starts to drop and not come back up with water changes then it is time to start dosing. The biggest thing when you start adding stuff to your tank is to monitor the parameters closely.