Depends on the coral and how long you have had 50 ppm nitrates. Some corals will do ok and even thrive in those conditions but SPS will over time brown out and die with that level of nitrates.
To keep this thread on track I picked up some warner marine eco bak pellets. I have 2 MR1 shorties chained together fed by a mj600. I am running carbon and phosban right now and thinking about which one to take out and which one to run first. I am thinking I will get more tumbling with the pellets in the first reactor but wonder if the carbon would pull anything out that was beneficial going back into the tank.
I have two separate reactors, one I still have the GAC with a MJ400, the other was GFO with a MJ600. I changed the GFO to pellets and changed to a MJ 1200. Are you thinking of running the GAC and pellets in series with one pump?