Hi guys. Im new in the hobby. I need some guidance. I have a 70 gallons acuarium with skimmer, sump system, plenty of media in the sump, overflow system, CO2 reactor and a whisper hang on back filter. All parameters are good except for nitrates which has been a battle since I started the tank almost a year ago. I did a 35% water change about a week ago, but a week later nitrates when up to 80. Any guidance?