Hello! I have a new 2 moths 200L old tank. I have 2 clownfish and 1 damselfish and some corals. The tank was thriving, everything in check. Yesterday I bought one beautiful boxfish. He was doing ok untill today. Suddenly he was falling on the ground heavy breathing, wanted to jump out of the aquarium spitting water and some other crazy stuff. After that all my fish started to breath hard, no red gills. I thought it was an amonnia problem. I rushed to make a big 50% water change and added some prime. When I almost finished the water change the boxfish died in front of my eyes. It was so heartbreaking… I have lost one shrimp too. Now the tank has a 50% water change done and 20 ml of prime added to it. The amonnia levels are 0 , nitrites 0, nitrate 10, ph lev 7,6 but the remaining fishes are breathing very fast. No white spots on them, no red gills. I know the boxfish can be poisonous when is dying but i removed him from the tank seconds after his death. Please help! I don’t want to loose anymore fishes