ALso suggest googling the assembly instructions if they don't come with the reactor: they have a diagram. Order of the sponges and plates is not intuitive.
IME using the bags is a no-go. Never works. The reactor can take a few months, and if it's not making a dent after a month, change the medium, and change it each month until you see a marked, significant reduction in problem. Phosban doesn't change color or indicate in any way when it's reached saturation, so to avoid spinning your wheels for several months with saturated medium, do the monthly changeouts. Less grief that way.