Koi acting a little strange, any help

Not quite a goldfish, but close. I've got a butterfly koi (Miyamoto) who has been clamping his dorsal(?) fin, except for when he swims really fast. He also had been kind of hovering near a plant with all of his fins clamped. When I approached the tank, he started acting more normally again, though his dorsal fin remains down. (not entirely odd for him) I can't quite describe it, but it just seems different than normal.
His fins have a slight tint of pink to them. Not sure if this is just blood vessels and is something I haven't noticed before, or if it is a change. I think, though, that it's more pronounced than normal. I see no fin damage, and no scale damage.
Ammonia is at .25 ppm at most (I'm really bad at telling the difference between color, and can't tell if the water in the test turned just plain yellow or has a tint of green to it). Nitrites are at 0, Nitrates are at 40 (still working on those darn nitrates, though they are slowly dropping.) I did a 25% water change two days ago and will be doing another one today, in addition to the normally scheduled one for tomorrow.
I'm worried about fin rot, though as I said there doesn't appear to be any actual fin damage right now. I just didn't know if anyone else had any ideas of what it might be. I may be worrying about nothing, but Miyamoto is my little pride and joy, and would like to catch any illness while it's still easily treatable.

 

Clamp fins are usually the sign of illness. What are the ammonia and nitrite now?

 

Actually, problem solved.
I posted a more in-depth description of what was going on when all of my fish started acting strange later that day. It turned out that something had been going through the alkalinity in the water, and the pH was skyrocketing enough to stress the fish.
Thanks though.
(Ammonia and nitrite both are zero. Nitrates are high, but that's because of the bioload on the tank. I am working on cycling the solution to that problem, as we speak)

 

The fish may be getting old, oxygen levels may be low, or it may just be tired.
I have goldfish who do the same thing. They aren't sick but they are very lethargic and move quite slowly. He may be sick. Signs of illness may occur but if not it should be fine.

 

The fish may be getting old, oxygen levels may be low, or it may just be tired.
I have goldfish who do the same thing. They aren't sick but they are very lethargic and move quite slowly. He may be sick. Signs of illness may occur but if not it should be fine.

Thank you.

As I said, though, problem was solved. I had a pH problem, most likely due to me not taking proper care of my tank combined with the koi producing too much waste.

Also, clamped fins generally aren't a sign of old age (though the others are, I agree)
Anyway, Miyamoto and He Who Eats Snails (my koi and his goldfish friend) now live in their own tank, and are soon going to get a 200+ gallon tank.