Probably the best for your system (LPS, Soft's and Clams) would be a Kalk reactor and a dosing pump. The CA Reactors are great, but IMO it's better start with the Kalk and add the CO2 reactor if you cant keep your Alk/Ca levels high enough. The added bonus is that the dosing pump will automate your top off so you can leave on trips in relative comfort knowing your salinity will stay constant.
There are some real nice units for a couple hundred dollars, or you can DIY for much, much less.
HTH
Glenn R