Help!! What's up with my Hippo Tang's fins?

I've been traveling for the past year for work way more than I would like, and unfortunately, it means that I don't have enough time to really enjoy my tank. When I do water changes and other maintenance, my hippo tang (like my dwarf angels) hides in the rock until I am done, so I never really noticed any issues.

I finally had a break yesterday and was watching the fish swimming, and noticed that the fins on my Hippo tang, which used to look "perfect" are really really bad looking.

I don't see any evidence of open wounds from other fish, and there is really no aggression in the tank. None of the other fish are exhibiting anything like this at all. He is nice and fat, swims around all the time, and eats like crazy.

Ignore the white specs and such in the photos, that is on the glass. I tried to color correct the images, so his color looks a little purple and spotty, but not in real life.

I've numbered the images 1, 2 and 3 to show different things.

1) Shows the top dorsal fin that I noticed first. Wow...
2) Shows some of the top fin, some of the bottom anal fin, and his tail that looks like a notch was taken out of it on the top with some issues on the bottom as well.
3) Shows the same as #2, but also wanted to mention that his pectoral fin on this side is actually curled inward at the top. Hard to see, but I wanted to mention it.

At night he crams himself between the tank's overflow and some live rock, so not sure if that is what caused the curled fin, but the rest just looks really wrong.

I've done numerous water tests and everything that I test for is in check. I have just a basic water test kit, but when I've had issues years ago, the test kit detected them as well as as they subsided.

pH 8.2
Ammonia 0 ppm
Nitrite 0 ppm
Nitrate 5 ppm (this used to always be high in my tank, but I've added a MarinePure rock about 6 months ago, and now it has dropped down nicely)

Any thoughts or ideas would be awesome. I've had him for about 4 years now and he is about 8" long (he is never still enough to know for sure.)

 

Thanks for the replies. I've been back out of town for work, but am finally home again. Carbon has been gone since about a week before the above pictures were taken. I'm working on a better way to feed nori too as it has always been a pain, so I've relied too much on algae pellets.

Currently I've got a 120gallon tank, and we knew at some point that the hippo tang would outgrow it, but our she is no larger than our purple tang (which is a good size, but not as big as what I would call a "large" hippo tang).

Maybe that time is coming for a rehome... Until then, I will ramp up the nori feeding as that is probably the key factor here if it is HLLE.