If you're set on a clacium reactor go for it. Many run successful reeef tanks with it. Some have trouble incuding a coincidence with crashes It's just not my preference.
This may help some pick a method or combinations for supplementing calcium and alkalinity.
In addition to salt mix via water changes and some dissolving of aragonite in the tank, there are 3 mainstream methods aquarists use to keep alkalinity and calcium levels in range( calcium 400+ppm, alkalinity 7 to 11 dkh).
Keeping the alkalinity more specifically the carbonate alkalinity constant is very important in my opinion particularly for sps. Calcium needs to be there in adequate amounts but levels above 400ppm can vary without harm, ime.
1) 2 part supplements.( commercial or diy) The Calcium part is mostly calcium chloride. The alkalinity part is mostly carbonate/bicarbonate.
You can dose them separately or individually. The calcium chloride will not effect ph.The alkalinity part will and should be dosed incrementally.
Some of these may contain small amounts impurities which is generally not a concern. Chloride will buildup over time but there is a ton of it in saltwater anyway (19,000ppm) so with regualr water changes it shouldn't have much effect on ratios. It is important to dose these 2 parts in proportions equivalent to those used in precipitation of calcium carbonate by corals,coraline and other calcifying organisms or as occurs in abiotic precipitation( the white deposits often found around pumps , heaters and other warm spots in the tank. For every 20ppm of calcium used ,50ppm/1meq l/2.8 dkh of alkainity is used.
2. Calcium carbonate via a calcium reactor. Precipitated calcium carbonate(the media) disassociates at low ph. The dissoved media provides clcium carbonate and calcium in balaced proportions. The CO2 creates acidic water in the reactor and the effluent and dissolves the calcium carbonate( media). As noted above variations in CO2 levels, media levels and fines in the reactor and flow can effect the amounts of alkalinity and calcium dosed at a given time It lowers ph too . Typical reactor effluent is under 6.9ph. So they require attention/monitoring . The media may contain metals and other impurites sunk in the calcium carbonate crystals that make up the media. These will release as it dissolves and could build up over time in a tank in organic or non organic forms.
Limewater(kalk) is calcium hydroxide. It provides a balanced dose of calcium and carbonate alkalinity .The amount you can dose is limited by top off needs usually around 1% of system volume and only limited amounts can be dosed in agiven hour to avoid ph spikes and a biotic precipitation.
The hydroxide binds with CO2 creating carbonate(the alkalinity) so it generally rises ph by reducing CO2.
It is self purifying . Virtually all impuities that may be in limewater precipitate out due to it's high ph. (12.4 at full saturation). It's as easy to dose from a top off container ,like a covered garbage can / bin or salt bucket. it strength for weeks without restirring in loosely covered containers.
