I started with just a kalk stirrer 6 months ago with my new tank. I have 20 frags and a 6 inch Derasa clam and kalk already can't keep up. If I don't manually dose, I'll drop 1 dKH in less than 24 hours. I have a calcium reactor ready to be set up, but just haven't gotten around to doing it yet.
You'll be fine for a little while, but in the end you'll need to dose or use a reactor IMHO.