About 2 days ago my main male Rainbowfish wasn’t himself, his fins were close to his body he was swimming on spot towards a corner of the tank I could instantly tell something was off. He wasn’t showing off to all the females and keeping the other males in check and he was very bleached out something was definitely wrong. I threw in food he showed interest but didn’t go up and eat, On closer inspection I noticed it’s barely visible (at the time) but when he’s looking towards you on his sides was a slim white/clear film, after these symptoms and a bit of research online I came to the conclusion that it has to be either Columnaris or velvet. I went to the LFS and picked up Red Sea Rally did a dose on the main display turned down temperature and gave the male a saltwater dip, today he looks worse very washed out and the film was alot more noticeable you can just barely see it now when looking at his sides. The only new things to the tank are 3 clouded archerfish who were in quarantine for a couple days but since nothing looked wrong with them, and they were eating every time I offered food I put them into the main tank. The tank is 75 gallons, pH 7.5, Ammonia 0, Nitrite 0, nitrate 5, and temp was around 80 but over 2 days dropped down to 76. Currently there are 11 rainbows (only 2 inches right now bought them as fry and am growing them up to get a good male to female ratio), Small three beacon pleco, 3 clouded archers, 4 bristlenose, and 1 sunshine pleco (Holding onto for a friend until the weekend), and a small panda Garra. He looks a lot worse today and I’m not sure what to do any suggestions?.