While I have no personal experience with Oceanic salt, I've read many threads regarding Oceanic and the slow increase in calcium levels overtime. The raising of the calcium levels depends upon how fast your tank is using calcium. If you have a high calcium demanding tank, it would take longer for the higher than normal calcium levels to occur. If your tank is a low calcium demand tank, you'll see the increase a lot faster.
If you've been doing regular water changes, add no additional suppliments, and you believe your tank is a low calcium demanding tank, then look towards the Oceanic salt. Try mixing up a batch to your desired specific gravity and test the calcium level of the new mix. If it's over 450, I'd say it was the salt. Some people have either changed to a different brand or have taken advantage of the higher calcium levels and have simply gone out and purchased another brand of salt that has lower calcium levels. Then they just do a 50/50 mix of Oceanic and whatever other salt they bought. Then they get a more desirable level of calcium with the new saltwater batch.
There is really no way to lower calcium levels other than wait until they naturally lower or perform a series of water changes with a salt mix that has a lower concentration of calcium.
Hope that helps.