Don't mix the salts. Your better off using up the remaining Oceanic (buffering if necessary) and then starting clean with the Kent salt. When you are are ready to do a water change with the Kent, you need to change over very slowly if you have sessile or motile inverts. They will be quite sensitive to the change and too much too quickly can be deadly.
Change much less water out for the first month or so. On a 225 gal
tank you probabley change between 25-40 gallons each time? For the next few weeks at least, only change Â½ your normal amount. After a few water changes have passed at the lower amount, slowly increase the amount changed each time until your back up to normal. This allows your inverts the opportunity to adjust to the new chemistry slowly and are able to adapt. It's not just alk
and pH but a miriad of differing elements between each salts makeup.