fish losing fins

[fdbum]

hi all i have a 54 gal bow tank with only 2 fish now in it. 1 is a trigger and the other is a snow flake eel. i had a lion fish. that got ich then it left and then it started to loose its fins almost looked like it was detierating and then it died couple of days later now my trigger is loosing its fins as well. what could cause this
is this a disese or what.
my nitrate is high but my ammona is ideal and my nitrite is safe ?
my nitrate has been high since the begining. i have no idea how too get it down tried everything and i should also say that this trigger has lived through alot of stuff.

 

[tiencvu]

I lost a blue hippo tang 2 days ago from ich. It got ich all over
the body and it lost its fins and tail and died. Don't know why?
Want to share the sorrow with you.
Wish I know the answer. For one thing, I did 25% of water change, the ich seemed to go away, but the tang didn't make it.
All the other fish in the tank seem to do fine now.