did something go wrong

I thought my angels were old enough to be okay fasting one day a week, and I don't want to overfeed the tank... so yesterday I skipped feeding, and this morning did a 25% wc, rinsing half the filter sponge. This morning I also saw with dismay that Zee, the smaller angelfish, doesn't have a straight dorsal fin anymore.

You can see Aiya here in the foreground, looks great (I think I even see the top filament on caudal fin starting to grow back).

Zee- smaller one on right here- dorsal is folded over at tip. I am upset, because I've read this is usually due to the fish growing up in crowded conditions. Do I have too many kuhlis, am I overfeeding, am I not changing the water often enough. Argh.

Aiya on the left: dorsal nice and straight!

Zee: not straight

full tank shot: