So I had a green chromis and it was doing fine for about 4 or 5 months then it started to only swim in the top corner of the tank for about a month, it would eat and thats about it. Wouldn't swim away if i put my hand near it. Didn't loose any color and had no visible spots. Then it disappeared. Couldn't find a body and none of my levels spiked or anything. Nothing in my tank could have eaten it. About 3 weeks later, 2 of my other fish (3 stripe damsel, and blue devil damsel) have started to do the same thing with the corner, but on separate sides from each other. There aren't any noticeable spots on both fish. I have no idea whats going on. My levels are all good. Is this stress or disease? Not sure how to solve this. Need help ASAP. Thanks.