ok....from my exp. fludised bed filters are excellent for nitrate removal..the key is to not use sand at all..instead biodegradable polymers (polymorph , PCL ,PLA) or you can simply buy bio pellets..i would recommend adding a ball valve to control flow to pellets..you want the pellets moving continuously but low enough to allow bacteria to grow on pellets..also i would direct the outlet of the FBO towards the skimmer for best results...this is the best method of carbon dosing (imo)..and all you do is add more pellets when needed..DO NOT GET RID OF THE FILTER..ITS A NITRATE REACTOR...