I currently have 150g tank that is 2 months old. NO Fish in it, just live rock, dsb and a sump w/live rock. Everything looks fine except the nitrate level. I am currently doing water changes with ro/di system. The water coming out of the ro/di system checks fine but the water changes are not lowering the nitrate levels. I am doing about 20-30 gallons per water changer every 2-3 weeks. Is there any other suggestions beside water changes to lower nitrate level?