I currently have a tank that was started about a year ago, and I only have one fish in the tank, a porcupine puffer fish. He is a messy eater, which might explain this, although the nitrates in his tank are like, 40-80 ppm. They're really high, and I'm really worried about my little guy and his nitrates in his tank. I do weekly water changes although the nitrates don't seem to go down. Any suggestions?