My sick discus

[Lewjo11]

Ok so I had my tank up for 5 month started with 2 then added 2 stunted ones 1 month later ( ya I got ripped off and they are aggressive as hell) then I got 4 more 1 month ago! All is good but the one original fish was picked on hard from the very beginning and has been off and on black color for that last 2 weeks! Today it was floating on side near death. It hasn't eaten for about 2 weeks or so. I had a 10 gallon tank around so I added it quickly and used the existing tank water to the tank along with the bubbler filter I had in the tank. Both tanks are at 85.5.
No white or puss fish. Only problem is very dark and tail is chewed a bit. Eyes fins clear and good! Yesterday and off and on color was about 60% nice. It's normal colors are blue and redish striping. It always had heavy black striping from the start!

What would be a good way to try and safe this fish!
Again it just seems abused! It will not eat

[jmf3460]

usually dark and not eating is a sign of stress due to water contaminates. what size tank, what are your water parameters (ph, nitrite, nitrate, ammonia) and you water change regimen?

[Lewjo11]

So my fish died my 2 newest fish one not eating since I got him 1 mouth. No sign of any issue except he is opposite side of tank when a feed them. And the other jerks around when swimming and had a super strong appreciate before but last week shows a black mark on one side. I did a water test today and amonia is 0 and nitrate is less then .25. I do 60 % water changes always and even a small one every morning to get a poop. Water sits 24hr before adding and 85.5 temp matches new a old water give or take .8 degrees.

I set up another 20 gallon tank and added my Spong filter and it had a smaller type of filter. I added 2 package of the API genral cure which has 250 mg of metronidazole and 75 mg praziquantel. Also I added a marinland all remedy. I plan to up the temp to 87 degrees.

Advice needed