If your specific gravity is that low that is why your Ca is so low. Stop dosing, correct your SG and your star polyps should open up. You need to be aggressive with your PO4. I would be surprised if a media bag alone will bring it down due to the high concentration. At the very least, you should be changing that media often (probably weekly or better) which will likely get expensive. Water changes are going to help to but they should be frequesnt and larger changes (think 30%ish+). Are you using man-made live rock by chance?