+ Start off with 1/2 box per 10k gallons (~40k L) for large pH changes (7.0 => 7.6); 1/4 box for small (7.0 => 7.2)

+ Check the page again; I believe I link to a French Canadian site that is selling them.

+ Don't worry about the calcium, till you have the kit. In any case, it won't be an issue if (a) you don't have a heater and (b) you don't add any more.