Unidentifiable White lump on a Corydora's Fin -With Pictures

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Aquarium Advice Apprentice
Mar 10, 2006
Hi, We have our female cory with an unknown white lump. Have looked at tons of pictures and text but nothing really fits the discription. Pictures attached as it is the easiest way to describe the problem. The lump is not like cotton wool or anything, it looks fairly smooth.

Tank details as requested:
Ammonia 0
Nitrite 0
Nitrate 20
PH 7.5
Temperature 25.5C
The tank is 60 liters and was set up about 6 months ago.

The filtration is Tetratec EasyCrystal Filter 250 and the EasyCrystal FilterBox 300. Unknown L/hour but the filter came with the tank

There are 6 fish in the tank: 2 corydoras:female 5cm = 2" long without the tail and male 3cm = 1.25" long), 2 male mollies: one 4cm = 1.75" long and the other one 2.5cm = 1" long and 2 female balloon mollies: both about 2cm = .75" long.

The water was changed 2 weeks ago (was planning to do a water change today as it is done wvery 2 weeks). The gravel is vacumed with every water change. . We usually remove about 25-30% of the water. The tank has some aquarium salt added to it.

We change the decor in the tank when cleaning every two weeks, but all the decor we use is their old ones and no new ones have been added for 5 months.

We feed our babies with frozen bloodworm, shrimp or mosquito larvae in the morning and a bit of TetraMin flakes for tropical fish (BioActive formula) in the evening (and King British Catfish pellet food for the corydoras). Their diet has been the same all the time.

These photos can be clicked on and enlarged.


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Is the fish eating and acting normally? It may just be a cyst or a tumor. Nothing you can really do about either, if the fish is acting and eating normally then I would not worry and just keep an eye on it.
Thank you for your reply.

She's acting, swimming and eating normally. The only abnormal thing is the lump. We spoke with someone from a fish shop as well and she said it could be a cyst or a tumor as well.

We changed some water and put a bit of salt in the tank, but we haven't treated it with anything else (because we didn't even know what it is). We're going away for two weeks today afternoon and we have a pet nanny popping in to check on the fish. He knows a lot about fish and does pet sitting full time so we'll let him know today about Albert's lump. (We've put an automated feeder as well - mechanical device, not floaty food.) Of course we're still worried especially when this happened right before our holiday.

If someone has any suggestions, please let us know.

Thank you.
I agree with Zagz, I wouldn't worry about it. Sometimes things like that just pop up and then dissapear. Sometimes it can keep growing to infect the fish, but I wouldn't add any medication to the water, because it probably won't do any good, honestly. Some people may argue that heavy heavy antibiotic use may help kick it, but I wouldn't use those unless you can be home to constantly monitor water quality.

With the way the cory looks, I'd say you have nothing to worry about. Of course no one can be sure of that, but that's just my opinion.

Thank you all for your help.

The lump is now almost gone and the cory is still fine. So thank you again. Your advise made things so much better. We didn't give any medicine.

Regarding the lump above in the discussion: our cory still has it on the fin, but it's about 1/3 the size it is in the photos above. The problem is that it seems to have got stuck in that size and is not going away completely and the more worrying thing is that now she has a second one on her anal fin. It's about the same size, possibly a bit bigger than the other one so not as big as in the photos above.

She seems fine otherwise, but I'm worried about these lumps. Something I though was if it is possible that it would be some kind of a body fluke (a bug) that builds a shell around it.

I don't think they're tumors as they appear so quickly. First I thought the first one was a blister or a cyst, but they should be going away.

Any opinions for what the lumps could be?

Thank you.
Hmm, doesn't sound like a fluke, no. If it was you'd see more of them and on the other fish too. If they start popping up more often, you could try an antibiotic in the water to help...which it may or may not do. Be careful with antiobiotics however, sometimes they can ruin your cycle and cause ammonia spikes.

Sorry, I don't know what else to reccomend. :(
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