I noticed that my guppy was swimming at the top of the tank the past two days unlike the others swimming around happily. Today I realized his back end was sinking till he was vertical and then would swim a little to straighten out. I know he is not doing well because he is not eating either, my only concern is could this affect my other guppy’s? What should I do with this guppy? I have separated him just incase but I don’t completely know what's wrong and I am unsure what to do. Pictures are attached to show what is happening.