Yes, Puffer: if you get alk and mag, get your alk to about 2.79, get your cal to about 400, and your mag to 3x the cal. Use the appropriate supplements: you already know you're low in cal, so you can buy that supplement (Kent is good) and add that. Wait 24 hours to test. And keep a journal of water chemistry, listing how it tested and what you added and when you did a water change. This will show you a lot. Once you get it in balance, which may take a number of days---you can learn which marine critters warn you of trouble. A fish that's particularly shy when alk is low. Mushrooms that contract when cal is down. ---And no matter how tempted, do not add more additive than is recommended on the container. You cannot rush it: wait 24 hours before testing, and test before adding more. Chemistry is a futzy thing, and though you may think you don't need to test before adding---sometimes a change will cause another chemical to come 'out of solution' and your tank will magically seem to manufacture something you thought you were short of. Test, test, test.