I recently got rid of a crawfish because he started attacking one of the goldfish and I didn't have a seperate tank for him. I've had both the goldfish and crawfish for over a year and the crawfish never attacked any of the other fish before, which I think the reason is he's gotten bigger and more confident. My goldfish's fins are healing nicely, but for some reason just this morning he started acting sluggish. He's barely swimming, just letting himself float around aimlessly in the tank. I don't know if maybe he has some internal injury I didn't know about, or what's the matter with him. All I know is I don't want him to die. Please give me some good advice.