sick fish large paccas i beleive

Question
I was told they are (paca)or poss pacu cousin to the peronna, they are about 5 to 6 in long really wide and big face,there grayish and silver little orange on belly near fins,in a 55 gallon tank w no other fish,I've had a little over a year,i do about a 1/4 water change when i change the filters about every 3 months.the white is not cottony its just there skin turns so white and there eyes go blind looks like it could peel right off. skin kinda looks mushy as it's like getting ate'in off... you can see it waving around them while swimming... ill treat goes away always comes back...when i have had other fish (Oscars')they don't seem to get it...thanks

Answer
Hi Jeannie
Sounds like you have a red bellied pacu.  Were you able to look at that link I sent about the pacus?  Has some good info on there about them.  You're not going to like what I have to say, but I'm going to be honest.

First, those fish get to be 2-3 FEET long, and fairly wide as well.  You'll need to have at a minimum a 250 gallon aquarium to accommodate them, and I'd say with the two of them, you're better off with a 300 gallon+ tank.  The old saying, oh a fish will only grow to the size of his environment is wrong.  There's a fish hormone, that tells the fish to "stop growing", but the insides/guts of the fish don't stop growing, and you'll see some fish that are really thick.  This is stunting, and it's painful for the fish, and shortens their life span considerably.  

Here's a quote from that site I sent you:
"My Pacu is 17" and I believe almost 3yrs. old. When we first received this fish from a friend at approx. 7", he was mistakenly Id'd as a Piranha. He sure looked like one!"

http://badmanstropicalfish.com/profiles/profile86.html

I'm not familiar with the exact growth rate of pacus, but I do know they grow fast.  I'm not sure if yours are on the right track with that, but this one grew 10 inches in  3 years....  That's a lot of fish lol.

One thing to think about, are you going to be able to get a 300+ aquarium for those fish, probably within a year or so?  Will your floors be able to handle that kind of weight?  Do you have a basement?  I've seen a few people make nice ponds in their basement.  These are some of the things you're going to need to think about if you want to keep these fish.  If you don't, you'll need to get them healed up, and start looking around for someone who can properly care for them.  You could try an aquarium, but they don't usually take fish in.  They usually have enough that other's have donated, and they have to be careful of diseases.  If you do give them away, you'll want to be sure the person/persons are aware of their potential size as well. If you want to keep them in a tank, and plan on/are able to eventually go with an extremely large one, you could upgrade to a 75 or 120 gallon now.  Get that up and running, then sell the 55, and use that towards the bigger tanks.  

Now, as far as the disease treatment.  You're not doing enough water changes.  You really should be doing, I'd go with 30-35% once a week.  You can still change the filter pads out every few months, just rinse them in a bucket of the used tank water every 2-3 weeks.  Never do it under the sink tap water, the chlorine will kill of the beneficial bacteria on it.
 
Not sure on what kind of filtration you have, but I'd recommend having at least 1 of the largest HOB's (hang on the back) filters(I like Marineland or Penguin with the biowheels) and I'd run a canister filter as well.  I'd buy that oversize as well, so it could be used on a larger tank.  

As far as their "disease", I think it's an excess buildup in their slime coat, due to the poor water conditions/not enough water changes.  That's probably what's also causing the cloudy eye.  They can lose their vision from the cloudy eye as well.  The excess slime coat is what's most likely the clear slime balls you're seeing on the bottom of the tank.  When the water conditions get poor, their defense is to buildup the slime coat to help protect them.
 
Do an immediate water change, the 25-30%.  Do this for about 3 days.  Then get on a weekly schedule like I suggested.  Also, pick up some aquarium salt.  Use that in the tank, dose it at 1 tablespoon for every 5 US gallons.  
But remember, salt does not evaporate.  The only way it's removed from the tank/water is through water changes.  So only add the salt back into the tank, if you're physically removing water from the tank.

Also, get the test kit to test the water parameters.  I think I stated before, you'll want your ammonia & nitrite levels at 0 ppm, and nitrates ideally under 20 ppm.

Are you familiar with the cycling process of a tank?  Where the ammonia is converted to nitrites, which are converted into nitrates?  Let me know if you're not, I can send you some good links explaining it.  That's why it's so important to do frequent water changes.  

If you don't see an improvement in the fish after a few days doing the salt treatment and water changes, let me know.  It sounds like what I said it was, the slime coat buildup, but there's also several other disease that are somewhat similar.  But due to what you've described, I'd put my money on the slime coat. I have one more link I really want you to read.  It's basically about this guy that bought a tank with a few fish in it that were stunted real bad.  It talks about their slime coat and such.  I just want you to get an understanding of how bad the stunting is for a fish, that's all.  It had pictures, but they're not working unfortunately.  

http://www.oscarfish.com/cms_view_article.php?aid=605

Again, if that doesn't clear up soon, or at least start to show improvement, get back in touch with me.  I bet you'll start seeing an improvement after a water change though.
Good luck!!  

Christy