German Blue Ram With Black Tail

[FishyFriend101]

Hi
Lately I've noticed that my ram has been hiding more often, but it was still eating so I thought it was just scared by my angel. Today I noticed that its tail was black from the end to just past the end of the dorsal fin. The edge of the dark area is not faded or uneven, it is just a straight line down and then it is the normal colour from there. There is still some red on the tail and fins, but it is very faded. The tail is not moving except for from the water moving it, and it is folded closed rather than spread out wide.
Thanks in advance

 

[SeanTrollope]

my guess is that it is sick or there is something up with your water

 

[FishyFriend101]

I thought that too, but wouldn't the other fish also be affected?