Tank is still new. Need to get your PO4 up. It should never be at zero. I feel like the problem you are having is that the coral you have placed are using it faster than you are putting it in. With the tank being so new your parameters are going to fluctuate regardless. Just feed a little more a little higher nitrate is not going to hurt anything just keep it stable and below 20. Try doing smaller water changes once a week. Say 1-2 gallons. This will help alleviate some of the problems associated with over feeding but all in all my recommendation is to feed smaller portions more often. Hope this helps. And good luck on your journey.