sick piranha

Question
hello,
i have 2 red belly piranhas . They both had eye cloud about 3 weeks ago. I treated them both with Metafix and they got better.
Now the youngest fish ( 5 weeks apart ) is swimming like it is disoriented , bumping into the sides of the tank , upsidedown swimming . it was even going around and around . This lasted a few days. He seems to have a rash under his bottom lip , it looks like little blisters . He is not eating , as far as I know . His sense of direction seems to be improving today . The other fish is fine , eating swimming normal , etc. I had the piranhas for 3 yrs in October - November.
They are in a 30 gal tank , with the proper filtration system .
I have some plants , gravel . I always keep the tank clean , about once every two weeks .
Should I remove the fish ?  I was thinking about taking him out , but i am not sure. I am hoping the other fish don't catch it .

Answer
I would discontinue Melafix.  It's garbage.

I would do immediate water changes.  35% today.  25% in 2 days.  25% 3 days after that to get new water circulating.

I'd check the water parameters.  Regardless of filtration, if media isn't changed often, it can be dangerous for water conditions.

I wouldconsider removing the fish in the meantime and putting him in clean water. :)

Happy fish-keeping and write back anytime.