I have had my 55 gallon goldfish tank set up for 2 months now and I was pretty sure it was fully cycled but now my nitrates are super high and no matter what I do I can't seem to lower them. I have two fancy goldfish and two commons in the tank. The water parameters are GH: 120ppm KH: 40ppm PH: 6.5 Nitrite: 0.5ppm Nitrate: 80ppm Ammonia: 0.5ppm The goldfish are exhibiting strange behaviours such as twitching fins, gasping for air, and occasionally darting around the tank. I also have 2 hornwort plants in the tank. Thanks!