The first thing I would recommend is that you get Salifert test kits for Ca and Alk, they are the only accurate test kits I have ever used and much much easier to read.
There are a few options in adding calcium, but you first must know your pH, alk, and Ca level because these are all related and adjusting one can throw the others out of wack.
Kent's liquid calcium is the easiest to use, but I believe it can throw your other levels out of balance.
the two part additives (b ionic) will probably be your best bet, easiest to use.
YOu may want to look into Kalkwassser, I use it and like it the best, but it has to be dripped in, so you need to read up on it before trying to use it. there is a thread, dripping kalkwasser 101 do a search for it.