If your tank is big enough or SPS/clam heavy, then you are better off using a calcium reactor.
If its a small reef or has fewer calcium-sucking organisms in it, then Liq. Reactor can work great. My tanks are usually low in SPS & I've had very good results with Liq. Reactor (my Derasa, Squamosa & Hippo clams have all grown extremely well). Sumpinfish & I seem to be the biggest fans of Liq. Reactor in the Lower Mainland I think.
HTH,
Anthony