High calcium correction.
 

After reading all your comments i went and bought another Calcium test kit. I now feel less worry but more stupid. My calcium reading with this new test kit shows result around 480 which is still slightly higher than average recommendation. Will this level be ok for my corals in the long run? I do appreciate all your comments.

These values are strangely high. Are you dosing any kind of additives to the tank (may be increasing your big 3).

Your secret is safe here.

480, although a little high, will be just fine. Let it drop naturally and test every 2 - 3 days until at a more comfortable level.

Much better than 1300-1500!!
Do as Warren suggests. Use my formula if you'd like to check how much your water changes will alter your tank parameters.
Otherwise, let it fall on it's own, but it will take a very long time without large corals to consume it.