At this point in the project I wouldn't be overly concerned about the nitrate level. Once fish are added we need to keep it down but since there are just plants for now high nitrates are not a problem.I have been doing 50% water changes everyday this week. (I've also been stirring up the soil on the bottom of the tank). So I have been trying. I'm at the point where I want to buy a mesh strainer and thoroughly wash the soil to see if this will help. LOL. They haven't gone down or up with a normal water change.