fry; damaged or disease?

[driftwoodhunter]

I'm posting this here instead of the fish forum because there seems to be more viewers here...

I have 3 crappy pics (sorry!) of a Columbian tetra fry about a 1/2" in size. I just noticed today the damage on it's fins - I'm really hoping it's from being nipped and not fin rot or some such thing! I have no way of catching it (it's in a 125g tank) and medicating a tank that size will cost a fortune.

There are a dozen or so of these fry in the tank - I removed 50 or so to a 40B to grow out. This is the only fish in the tank I've ever seen so far that isn't normal. It's also one of the smallest fry in the tank. It does get chased/nipped by the larger fry, and when all the fry were tiny, some were hunted down & eaten by Buenos Aires tetras.

I'd like to know what people think - disease or damage? The dorsal fin seems to be fractured midway, which also leads me to think damage (not to mention how badly I DON'T want it to be disease) the upper tail fin is missing. It's a clean cut off, no fuzz or fungus/bacterial sign that I can see. I've had columnaris in a tank before so I get very jumpy. I included a pic of a healthy fry so you can see that the fins are tipped in white while they are young. Has anyone had a fish that had part of it's fin bitten off? I am watching diligently now, but I'm hoping that's all this is.

Don't have tank parameters on me, I'll retest tomorrow. I should mention that there have been no new additions to this tank since I set it up about 4 months ago - all the fish in it came from my other tanks. I QT any new fish for 2 months minimum, and I have 12 Blue Tetras on order for this tank, but they will be in QT until Sept. Thanks for any opinions! (QTing the fish is simply not possible, I can't catch it)

Thanks! Pics:

healthy fry;



Damaged fry;

[driftwoodhunter]

Ok - tested the tank and got this;

PH = 6.5

Ammonia = 0

Nitrites = 0

Nitrates = 10 or 20, the API color chart looks identical to me : (
I think it's closer to 20

I did read that adding aquarium salt could be beneficial to healing, but I wonder if it would negatively effect the tetras or the plants? I have API salt on hand, as well as kanaplex, but I don't believe (perhaps wrongly) in medicating a tank without knowing the problem - I've never medicated as a preventative...

I also read, whether true or not, that a white edge to a damaged fin is the color of regrowth - that if it turns bloody, black, red, or grey that it's a problem. But I would think fin rot would look white too? Am I freaking over nothing? I tell you, columnaris puts the fear in you for sure! That was over a year ago and I get over-excited whenever I think something's wrong. (it wasn't in this tank, or with any of these fish)