The solution is acidic at this point and must be neutralized to precipitate MgNH4PO4-6H2O. Add15ml of ammonia to your plant food and Epsom salt mixture (using a graduated cylinder). The solution must be basic for precipitation to be complete. Stir well and test the solution with pH paper. As long as the solution remains acidic continue to add ammonia (in 15 ml increments) until a pH between 9.0 and 10.0 is achieved. A white precipitate of MgNH4PO4-6H2O will form. Allow the solution to stand for fifteen minutes before filtering.