PO4 must come from your miracle gro, that is the idea of using dirt, having PO4 for plants.
Sometimes a lot of nutrients can leach in the water column on the first weeks, maybe too much at the beginning. That's why it can be a good idea to do some big water changes on the first days.
Now that your PO4 are at 1,5 ppm, I would the leave the tank that way. That's good for the plants.
Last edited by micheljq; 07-29-2013 at 02:08 PM.