I left my 20g tank go dormant with no live fish for about 6 months, kept the filters running (u/g and penguin 300 bio-wheel) but no lighting. I revived it 2 months ago with a 50% water change, new additional lighting and a new Eheim 2213 canister filter to replace the penguin. The filtration provides incredible water flow through the tank. After the 50% change the water had -0- ammonia -0- nitrite but 80-160 nitrate. I left it run 2 weeks without stocking. Added an anemone and small hard coral and banded shrimp - all of which have been doing fine over the past 2 months. Over that time I also added a small blue tang and a week later 2 small clowns, all of which died within 10 days. I have been making weekly 1g water changes and continue to have extremely high nitrates, all the while adding regular and generous portions of Instant Ocean Nitrate Remover, which has done nothing. I checked my tap water and it has nominal nitrates. Why don't the nitrates go down?