Ca & dKh - How much is too much?!

[WhiteTang]

I keep seeing the term "stable" water parameters are critical for coral health!
But how much is a big swing?!

I have recently installed a 3 pump doser for Ca, Alkalinity and salts (light balling method by aquaforest called components 1,2,3).

I test everyday and my parameters stay within the acceptable limits.
Ca - 400-420
dKH - 8,0-8,3
But even with the doser installed I do get some swings in Ca and Alkalinity in the range of ~0,3 dKH and ~30 ppm Ca. My guess is that it has to do due to the lack of accuracy of the test kits / light conditions and not actuall swings.

But my question remains: what kind of swings are not within the "stable" zone?
Are we talking about swings if 1dKH /day or 0,2dKH?!

[Sapelo]

It sort of depends on what you are hoping to keep. Fish don't care so much about the swings you're describing, softies don't really care, but SPS would care.
Are you testing at the same time every day? Honestly you should not be seeing a 30ppm swing in CA although I don't know that it would be as bad as an ALK swing.
(your post is a little confusing, I assume you mean decimal points where you have commas?)