Put your ceramic media in a separate bucket with a bubbler for 8 weeks, doing water changes once weekly. That will kill off the parasite in the media. For your tank, which I take it is otherwise bare, drop in a jigger of Clorox, leave it for 10 minutes with pump running, and then empty it, fill it with fresh water (for economy), and add a double dose of Prime chlorine remover. Run it for 30 minutes, then empty again, and fill with salt water. This will clean your tank and kill any parasite remaining. Do not use your 'rock' substitute again until its 8 weeks are up. You could just toss it and buy new.
Meanwhile, set up a quarantine tank, and consider carefully whether you want to buy from that same source again.
Your nitrate situation could be coming from the water you're using, or it could come from food if the ceramic media are not strong enough to handle it. Managing a clean tank with bare bottom is going to need a filter sock to catch any food that might collect and contribute to the nitrate situation. You might make some simple ones out of white cotton for a very small pump outlet, designed more just to catch excess food, just a little bag and a drawstring, toss them when they stop being white.
