Cory problem

[dogdoc]

I need some help once again. How come the problems my fish seem to get don't fit the descriptions on any of the disease resources? Anyway here goes.

Noticed last week that one of my cory cats has what appears to be some type of cyst on the rear edge of his dorsal fin. It does not appear fluffy, or inflammed and there are no others visible on his body. None of the other fish have any either. Best way to describe it is that it looks like the fin itself has a blister on it. He's still eating and acting normally, but I have seen him flick off the decorations once or twice.

I know you'll ask, so here are the water params. pH7.2, amm 0, nitrite 0, nitrate 5, GH 3, KH 3, temp 77-78. Tank has been up and running for about 3 months and I do water changes of 30% about every 5 days.

Weirdest thing about this tank is that the supposedly delicate fish do great. My neons are thriving, my other tetras are fine, even my clown pl*co is doing well. But I have had trouble with the reportedly hardy molly's, and now my cory is giving me trouble. The other cory of the matched set also has no problems.

 

[TLH]

Is it like an ulcer or a growth?Fish do suffer Cancer sometimes and some things are hard to diagnose anyway until it's too late.If you could get a pic it would help alot.
Mollies appreciate some salt in the water.Have you any?

 

[dogdoc]

It looks like a growth, definitely not an ulcer and it does not look like any of the pictures of the common fungal or bacterial diseases that I have checked out. It almost looks like a bubble of some kind in the fin, only slightly more opaque.

I do have some salt handy, but I am hesitant to use it, because I have heard that corys and pl*cos do not tolerate it well. Don't know if that is true or not though.

 

[TLH]

I only have one Cory atm which has stood 2 teaspoons salt per gallon for extended periods.I used to have Mollies a while ago.As for your Pleco,who knows what they can stand.
Your Cories abnormal growth may not affect anything adversly.If it's happy and eating OK I wouldn't worry too much.Keep an eye on him though because if it dies in the tank(worst case scenario)you don't want to leave it for the other fishes to eat.
If you can get a picture of the area post it up

 

[TLH]

Lookee here at this link.Scroll down to the pic of the Cory and read.
http://badmanstropicalfish.com/disease.html

 

[dogdoc]

Thanks for the link TLH. If that is what mine has, he has a minor one. Nowhere near what is in those pics. I do wonder though.. We did lose power overnight last week during a big snowstorm. Temp in the tank got down to 70 and there was no filtration or aeration overnight. Now I'm trying to remember if it was there before that or not. He still seems to be doing great, and I think whatever it is has gotten smaller. I'm keeping my fingers crossed.