Brian, Ideally what you want is to replace ALL your evaporated water with calcium saturated water (Kalkwasser/limewater) this will hopefully kill a few birds in one shot, it will top off your water, provide it with the depleted calcium, maintain your ph stable and other things that are beneficial to the tank.
In most cases (lightly to medium stocked tanks) kalkwasser will be sufficient to keep up with the calcium demand, however when you get into heavy SPS's, lots of coraline etc, you may need to supplement further by means of a calcium reactor or manually.
The drawback with Kalkwasser is that at saturated levels it has a ph of 12, the good news is that your tank natural buffer system can stabilize this high ph, the key is to dose slow to avoid sudden rises in your tank ph, usually a slow drip from a container works fine but it is high maintenace cause it clogs often and you need to mix and refill daily. (not for me)
One of the easiest ways to dose Kalkwasser is through a Nielsen reactor or Kalk reactor, this is simply a container that mixes your kalkwasser powder with the ro/di water before is dose to your tank.
I usually can fill my reactor with the powder and forget about it for a couple months, the reason for this is that kalkwasser does not dissolves further inside the reactor when the water has achived saturation level (PH 12)
Your current setup is fine to integrate a reactor but you can not use a float switch at the end because with time it is likely to accumulate calcium deposits at the seal and leak.
switch
