Red tailed shark is flashing?

I have had the shark for about 3 weeks now and have had no problems up to this point. For the last week or so the shark has been losing color slowly. No spots on the shark but the gills are a bit greenish since I got it. Yesterday got water checked and everything was ok so I got 2 yoyo loaches to add to the tank. He was aggressive for about 2 hours then the shark started to rub against them. Then I noticed the shark was flashing and flipping in the water. Tank stock 2 silver dollars, 4 zebra danios, one red tailed shark and 2 yoyo loaches.