I just put an XP2 on my 30gal and Personally I love it. Is your flow on the spray bar still the lowest? I Found that my XP2 actually cleaned my water better that that of my AC50 that was on there. I actually replanted my whole tank the same night i put the XP2 on there so there was plenty of debris in the water and a few pieces of drift wood so plenty of tanis also....but the next morning i work to find the cleanest tank I have ever had. I have just the filter pads and carbon, plus the phos-sorb pad, bc of high phospates and silicates in my water at home. I would possibly try turning your spray bar wide open to keep from restricting flow through your filter. Thats the only thing that I can think of right now. I dont know why you would have any problems, i found that mine actually helped my problems. And i did as you and put part of the filter media from my AC50 in the XP2, but i did keep the AC50 running, just for extra support biologically, so that could be part of the problem.