Is this how gill rot happens?

[twentynineriverside]

The past week my new Geophagus Jupari fish has become ill. The behavior is lethargic but not alarming in itself. The worrisome part is the open wound which has developed on his right gill. It started looking like he scraped it but has now grown into an open wound which is red and even blackish in the center. At first I just thought he had scraped it but it has deteriorated and he just sits facing the corner most of the time now.
I won't bore you with how I like this fish and don't want to lose him but the feeling is there.
The tank is a 125g freshwater/south american set up about 1.5 - 2 months. I change about 20% of the water weekly. The tank was recently (2 weeks ago) attacked by the worst Ich and red algae I've ever seen while I was gone for two weeks but I've nursed it back to health since then. The PH is between 7.5 and 8.0. My local water is 7.5 and due to a filter previously used in a saltwater tank it goes up to about 8.0 in my tank. The water has a medium high GH.
I'm posting pictures but unsure if they'll go thru 'cause I've never done this before. The tankmates are geophagus surinamensis, EBJD, BGJD and red hump geophagus.
Please let my know if you have any advice. I cleaned the tank, changed the water tonight and added extra salt. Thanks for any help you can offer.

 

[FishingOut]

Looks like an extremely bad infection. It might have started with a little scrape that got infected, But I think your at the point now where you need to take action.

Have you been useing salt? 1tbs per 5 gallons.

If that hasnt had any effect you will have to resort to meds. Id suggest a good anti-biotic. melafix heals up wounds and ulcers very quick.
Good Luck and

 

[twentynineriverside]

Thanks, will try

 

[twentynineriverside]

What i should have said is yes, I've been using salt, not really measuring it but adding it when I do water changes (mostly weekly but biweekly occasionally), roughly estimating it. How often should I be adding salt?
You don't think it's gill rot or something contagious? I've been an aquarium hobbyist for about 5 years so I'm not totally new but I've never seen this kind of thing before and don't really know how to deal with it. I'll try the melafix and check out what other products are available.
I do appreciate your response. Thanks.