So today the water in my fish tank was changed. I got a siphon and removed about 50% of the water so that it could reach the bottom to clean the gravel. I have 4 fish in there (pleco, loach, goldfish, and koi). The water ran straight from the tap. I then checked an hour later and my Butterfly Koi is in one corner of the aquarium floating sideways with it's mouth open. It also doesn't seem to be moving. My other fish are huddled together on the other side of the tank. Is my Koi dead, or is it just stressed out?