Hi there, I just got in to the hobby and purchased a fully set up 180 gallon tank secondhand. I am using all of the original water and rocks with new live sand. I got the tank about a month ago and have have been dealing with extremely high levels of nitrates. The tank was definitely slightly neglected when I bought it but it had 7 fish in it that are still alive and doing well but I would like to add more but not until I fix the high nitrate problem. I have already done three 30% water changes and honestly the levels seem like they are almost getting higher. I have been using test strips to check levels and I can’t exactly tell what the exact number is but it is somewhere between 100 and 250. All of the other parameters seem to be right where they should be. Any advice will help. I am looking to resolve this problem relatively quickly, thanks