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Betta with Fin Rot and Lump on his Side

Krystle D

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Hey Nerms,

Aquarium Parameter information

Ammonia: 0

Nitrite: 0

Nitrate: Between 20 and 40 ppm 

Temperature: 80

Tank size: 5 Gallons

Water changes: 50% once per week

Relatively heavily planted, dosing Easy Green, K, and Trace twice per week


So here's the situation:

For a reason I didn't know at the time, all of a sudden fin rot appeared on my betta’s tail, pinholes that quickly resulted in tears. So I did the Coop-recommended treatment of Ich-X and Maracyn for 7 days. In the middle of this treatment, I did a casual strip test for Nitrates which also tests Nitrites, and was shocked to see Nitrite!! I got my liquid tests out and confirmed there was 0 Ammonia but 2ppm of Nitrite. Now I am realizing that the fin rot probably set in because the poor guy was living in Ammonia and Nitrite-ridden water without any Prime to detoxify the Ammonia while the cycle re-established (ugh!). So since that treatment was still going on, I dosed 4X Prime to detoxify the Nitrite, daily, so any further infection coming from the Nitrite exposure wouldn't happen, and so that the treatment could run for the 7 days. The tank is now completely re-cycled (cycle crashed because the filter pump broke and I didn’t realize it for a few days), however I still do daily tests to make sure. Now shortly after realizing the Nitrite was there, I also noticed another, more troubling thing going on. On my betta's left side, there appears to be a lump. It is right behind the stomach, and only on that left side. there is no open wound at all; it seems that something is swollen on the inside and pushing out. I am just at a loss for what this is, and I figure it can't be anything good. Looking at some betta anatomy photos, it appears to be right over the kidney which has me wondering whether this is perhaps a very early sign of dropsy, perhaps even a tumor?

After the 7 days were over and a 60% water change, the fin rot hadn't progressed, but also hadn't gotten much better. So I decided to do a full round of Maracyn for the 5-day treatment (according to the instructions on the box) to really kick the fin rot in the butt. So far I am seeing most of the fin rot go away, and healing is already happening. But at this point my main concern is this lump. I have scoured the rest of the internet and can't find anything similar enough, so I figured it was time to get some Nerm input!

The lump hasn't gotten any bigger or smaller since I noticed it. I also want to emphasize that my betta's behavior and eating habits have not changed at all throughout all this recent turmoil. Still very active and very eager for his food in the evening.

i wanted to provide this background of what has happened recently with the poor water quality and fin rot in case this has something to do with this lump appearing. What is this lump???

Please see these images below, the last one I posted is of him before any damage and fin rot to his beautiful tail, so you can see just how much that fin rot very quickly deteriorated his tail. LESSON LEARNED with that pump! I tried to get some good top view photos as well. Please let me know if additional photos are needed!


Thanks for your help Nerms!









Edited by Krystle D
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Most of the time fin rot is caused by poor water conditions I would Qarantine and treat with aquarium salt 1 table spoon for 2 gallons for 1 week  best defence against fin rot is regular water changes and good water conditions 

Edited by Colu
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13 hours ago, Colu said:

Most of the time fin rot is caused by poor water conditions I would Qarantine and treat with aquarium salt 1 table spoon for 2 gallons for 1 week  best defence against fin rot is regular water changes and good water conditions 

Thanks Colu! Yep I am certain the fin rot came about due to my cycle crashing after my pump broke without me noticing it for a few days. So definitely making sure the water quality is good with daily tests, but the tank is now re-cycled so just a matter of time for the fin rot to be fully kicked.

So my main concern now is that lump on his side. Any ideas what that could be?? I wanted to make sure to provide a background of these recent cycle-crashing events and the fin rot in case that has something to do with it.

What in the world is this lump??

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It could be a tumor, or a cyst. The best thing to do it keep the water clean and just monitor. If it is a cyst it could rupture, and you would need to treat with meds. 

I have a betta with tumors on his head and gill covers. They just slowly grew over the years. They don't affect his behavior, and he otherwise seems completely normal and active. Sometimes he bumps the one on the top of his head, and it bleeds a little, but I just make sure the water is pristine and it heals up fine. 




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