Well there are a couple of ways you could go...
Two part dosing using either BRS or similar. Measure the uptake and then drip dose accordingly.
Kalk. Ideally with a PH probe, work out how much your uptake and use a reactor to dose in auto-topoff.
Calcium Reactor. Again with a PH probe. Considering the tank is 30 gallons, it would probably only be needed with an extreme amount of SPS.