That's a good point Loach, maybe there is a lot of flow? Angelfish catch the drift like sailboats and will need to move their pectorals all the time to keep in place.
About the koi thing, these are not koi angels, they are gold and gold marbles. Koi will not have any horizontal striations in the dorsal fin, it will be clear. As young angels, their gill plates will be thinner (pink tissue shows thru) and transparent, causing a blushing cheek area. As the fish matures, the gill plate hardens (pink colour sometimes fades completely) and patches of guanine deposits randomly express on the body.
Here's my blushing platinum as a young angel. Not a koi because it doesn't have a marble gene and two blue genes make it platinum, but you can see the gill plate has not hardened and there are no striations in any of the fins.
From what I know about septicemia, there is a bacterial type and viral. I strongly recommend you test the water, there are test kits available to order. But if it's viral, there's a chance the fish have it for life. If params and conditions are kept up, the fish can live years and it can sort of go into remission. For bacterial septicemia, the fish would suffer more and not last that long. Since all of them have it, it's either a play with the camera/ lighting or viral septicemia (I would say).
