If you are getting high readings coming from effluent then one of two things are going on. One, need to reduce flow rate until bacteria populate. Two, not enough media to handle the load. Something that helped me out to start is that I put my sulfur media in a one gallon container and poured tank water to cover and let that sit there for about a week. I think this jumpstarted the bacteria and my "break-end" period was less than two weeks with getting zero nitrates out of the reactor.