I used Miracle Grow Lawn (water soluable) with a small mix of Green Light liquid Iron last summer with excellent results!
Actually you don't even need to go to that trouble. Just hook the one zone on the fertigator to the common valve line on your sprinkler system. It will then use that line for all of the zones that don't have a connection to a fertigator controller zone. I've had mine wired this way for 2 years and no problems. I love this product, as long as I put down a heavy granular dose to start the season!