OK...to do this right, you need to know a few things.

Hmmm, not on my computer right now...don't have my bookmarked pages...I will post that later.
For now, *If you are going to add calcium you should have a calcium test kit as well. *Generally accepted leves are about 400-450.
You will also need to keep alkalinity up as that does affect the ability of organisms to lay down calcium....I think that should be *9 -14 dKh...again, you will need an alkalinity test kit.
Finally, if you have problems maintaining either of those parameters, you should check Magnesium, that should be 1300 - 1400.
These are all forms of salts and can be overdosed so make sure you test before you add. Additionally, if overdosed, you will get the opposite effect as it will spontaneously precipitate out of the water

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Sorry! *Hope I did not give you too much info at once! *I will try and get those articles posted for you later that go into more detail...If you look under the chemistry part of this forum, you will find lots of related articles.
It's not really difficult or complicated...don't worry!