Does my angelfish have finrot?

2 days ago I noticed my one remaining koi angelfish was acting weird. Yesterday I noticed he was moving very slow, he still eats normal but has trouble swimming fast like he used to be able to. When I used to come up to the glass, immediately he would come see me. Now he only comes up half the time and very slowly when he does. After close examination I noticed his caudal fin was jagged on the end and his dorsal fin was split down the middle. Today I noticed his right pectoral fin was also torn and he wasn't using it much. I think this is finrot and if it is how do i treat it. I can't use anything with malachite green since I have chemical sensitive catfish. Also if it is finrot will it spread to ay of my other fish since he is my only angelfish? If it is any help my other angelfish died a few weeks ago but had no signs of any fin damage. What should I do, he acts normal but is slow and partially crippled?!?!

Aquanero said:

Can you post water perameters? Ammonia, nitrite, nitrate, Ph and hardness. What is your maintanance schedule like?

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Ammonia: 0
nitrite: 0
nitrate: 70 (I'm doing changes more often so it's dropping, doing one later today as well)
temperature: 78-79
ph: 7.6

I just did a 50% gravel vac so hopefully that helps some.

I'm doing weekly 50s now since they don't see. To go above 40 or 50 by the end of the week. He doesn't seem any better though, if anything worse! Is there anything I can do to help this?