Can’t identify this betta illness- Black patches??

Aude Lefranc

New Member
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3 years
HI all,

I need your help identifying what’s wrong with my betta. I had my previous betta for 3.5 years and it never once got sick (it ended up dying from the shock of moving cross country) so I’m not equipped to handle this.

I got this guy from a local pet store in August and it’s been struggling with fin rot ever since. Also got another betta (In an 8 gal) from the same store and it got a cloudy eye within two days, so there is obviously something up with that store. But more recently, betta #1 had black patches show up on both of its sides. The fin rot hasn’t progressed for a couple month, but also hasn’t really healed. But I’ve never seen black patches on a fish before!! Is this a sickness or some kind of unusual color change?

The tank is 5 gallons, filtered, and cycled. It isn’t heated but my house is 74-78. The ammonia and nitrites are 0, nitrates are 10. I keep almond leaves in the tank. I’m currently treating with kanaplex because I figured it would help a bacteria infection. Also previously treated the fin rot with aquarium salt but that didn’t do much. The fins have looked like this for months. They aren’t getting worse but they aren’t growing back.

Any thoughts?



Active Member
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5 to 10 years
Hi, this is super interesting. One of my bettas had the exact same condition where the entire area near his tail turned black. It never went away but it didn’t seem to bother him at all. He live his entire life with that black patch and finally passed away as a crotchety old fish.

A quick google search gave me a few ideas that look very similar to your fish.

1) There’s a condition that occurs in wild bass called melanosis, where the skin produces black pigment in response to sun exposure.

2) “black smudge” can occur in goldfish and other aquarium fish when the water is very high in ammonia, like a chemical burn of sorts. High levels of bacteria or generally dirty water can cause it. Either way, the black spot is an indication of underlying problems and doesn’t really hurt the fish directly.

3) sometimes the introduction of aquatic snails can cause black patches. Lol you don’t have snail do you?

I honestly don’t have much experience with that, good luck friend. As for the fins though, just make sure it doesn’t get worse or infected. I had a male that bit off his fins until they refused to grow back. He seems much happier and more energetic after though, so it’s really not a big deal.


Active Member
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I've been dealing with fin rot, first in a betta I took in that had a severe case, and now in my main tank due to cross contamination.

My betta had similar dark coloration, it didn't seem to hurt him. But I don't really know much about it.

As for the fin rot, have you ever tried Methylene blue? ? A common treatment is performing a methylene dip, where you net the fish and dip it in a methylene solution for 10sec. That's what I did for my former beta, and it seemed to help. But he was a far gone case. If you are worried yours still has fin rot, a few dips in methylene might be just the thing for it. You can also do prolonged baths in lower concentrations.

You can also do 30 min aquarium salt baths with or without blue. Just make sure the temperature is equal to its home tank, and that all the salt fully dissolves so it doesn't burn your fish. But I believe that article covers most of what you will need to know about dips/baths.

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