exactly, your filter can't turn the ammonia to nitrite quick enough. time for a bigger filter or more of them. try to get 10 gph per gallon of tank water.grosse gurke said:You need to add more bio-filtration. If you add a canaster filter you will not have this problem. I have 3 canasters on my 125 with eight good size very messy pygos and I have never had a problem.