URGENT: Please help, sick skunk cory

[kschaf012]

My skunk corydora is in bad shape.. i'm not sure what's wrong with him and need advice ASAP! About 2 weeks ago, I noticed that the barbels on one of my skunk corys were almost gone (they are very short and stubby compared to the other cory). He was still eating and seemed okay otherwise, so I kept a close eye on him and did pwc's every other day for a few days. A week later, I noticed that his anal fin looked damaged quite a bit..he still seemed to be eating and acting normal. The ammonia in my tank was 0.25 ppm, and nitrates were between 5-10 ppm, so I started doing pwc's with prime and vacuuming the substrate daily and continued to watch him closely.
I was out of town this past weekend, and Sunday when I returned my cory looked considerably worse. He seems to be getting thinner and is not showing interest in food anymore. I am definitely seeing redness in the gill area and also on the fish's underside/belly where his fin is damaged. He is losing coloration on his face, it almost seems like the black areas under his eyes are turning a cloudy white? Could this be some sort of fungus? bacterial? Could the redness be a sign of red blotch disease? The redness definitely seems to be internal. The other cory appears to be slightly red, but definitely not as bad as the other guy.
I tested the water today-- ammonia is still at 0.25 ppm, nitrates down to 5 ppm. I have been doing partial water changes almost daily for a week,I am not sure what else to do.. is it the ammonia causing these problems? Or could this be something else? Aside from the daily water changes, how else could I get the ammonia to go down to 0 ppm?

My fish looks very sickly and I am really worried about him and the other fish in my tank.. does anyone have any suggestions on what I should do?? I am at a loss.. i'm afraid if I don't act quickly he is not going to make it much longer.. ): I do have Furan-2 and Prazi Pro.. but I don't want to try and treat the wrong thing and harm my fish even more.
My tank is a 17G planted tank with sand substrate, I also have 2 otos in there as well. I dose the tank with prime during every pwc. My tank has been set up for about a year now. Here are all of my current tank parameters:

Ammonia 0.25 ppm
nitrate 5 ppm
nitrite 0 ppm
pH: 7.2
temperature: 74° F

I'd appreciate any help/advice/suggestions, I really don't want to lose my fish ):

Here are some pictures of my fish.. the first 3 are the most recent, you can see the redness and discoloration on his head. In the 3rd picture with the flash, I was trying to get a picture of the whitish area on his face that I mentioned.
The last 2 were taken a week ago, but you can see the damaged barbels and damaged anal fin.

[littletoot2016]

The redness is an ammonia burn, the white film is the fish producing a slime coat to try to protect itself from the ammonia. If you dose Prime in a 3 to 4 times dose it can help. When you vacuumed the gravel did you get a lot out? If so do it again. It sounds like you have an infection started so Furan would be the drug of choice. I would do it in a 1/2 dose. You need to remove the plants because Furan will kill them. I would stop feeding for 3 days, this will help your ammonia problem. Let me know how it goes, Harry

[kschaf012]

I did pwc's (and vacuumed the substrate) almost everyday for about a week and a half, and I also dosed prime, and decreased feedings. I was able to get the ammonia down to slightly below 0.25 ppm, but I haven't been able to get it all the way down to 0. I am currently treating the tank with a second round maracyn 2, so I can't change the water again until the treatment is finished. The guy at my LFS did say that the API test kits could give these very low ammonia readings as false positives...

The redness has gotten worse, the area on his underside almost looks as if it is bleeding or an open wound or something, it is very red. He is also breathing a bit rapidly. AFter the first round of maracyn 2 treatment, he is a bit more active than before, but his behavior still seems abnormal to me, like he is acting restless/skiddish.. a few times I have seen him slowly swim around in small circles. He is still not showing much interest in food.

Could this be another issue other than the ammonia? I could be wrong, but Isn't furan used to treat fungal infections?

[Coryman]

Certainly a water problem, I am certain it is nothing parasitic, but bacteria will infect damaged areas.
The first thing I would do is make a large water change 75% and then add a full dose of API Melafix. The red blotching under the scutes is hemorrhaging most likely caused by nitrite burn. Quite often there will be a nitrite surge, but by the time the effect shows on the fish the levels are back down, but the damage has already been done. The barbel degradation can also be a result of nitrite surges, but more likely from high levels of Nitrate.
My motto is always "If in doubt change water" but regular water changes should be made anyway, and a good varied diet.

[kschaf012]

Thank you for the reply coryman. Unfortunately, my cory did not make it...he developed a bright red spot on his side behind his gills (almost looked like internal bleeding/hemmorhaging of some sort) over night and died shortly after ):

I now have only one remaining cory...who is also unwell, however he seems to be showing different symptoms. He began swimming very erratically, very fast up and down the sides of the tank repeatedly for long periods of time. He has kept this up for weeks now, it seems almost everytime I look now he is darting around the tank.. he has never done this before. He has also stopped eating, I've tried hikari wafers, frozen bloodworms and frozen brine shrimp (used to be his favorite) to no avail. Although it is hard to get a good look at him (whenever I try to look closely he swims away), his entire underside seems to have turned entirely white, and there is also a small area of white on the side of his face. It does not look fuzzy to me like fungus, i'm not sure if this is something with his slime coat, or some type of infection? More recently (about a week ago) I noticed a tiny chunk missing from the bottom of his tailfin.. I don't see any redness in the area.

I have tried melafix, and just finished treating with prazipro (someone suggested it may be a parasitic infection), both did not seem to work at all. My nitrates are very low at 5 ppm and ammonia is still 0.25 ppm, I have also been doing large pwc's, nothing seems to be working. I know he is probably unhappy/stressed because he is lonely, but I don't want to get more cories if there is something in my tank that's causing these problems. I am at a loss, I really don't know what to do at this point..it seems I have very bad luck with these guys ):