Sudden Loss of Tail Fin!! - Koi Betta

[caillouscaillous]

Hi! I've had my Koi betta for about 7 months. He seemingly lost a large chunk of his tail fin overnight? (I look at him every day, and today is the first time I've noticed it. It's a huge change so I think I would have noticed immediately? I'm not sure though). Here is a comparison photo of his fins from when I got him versus now. He has gotten larger and slightly darker, but his back fins were full/fan-shaped and at parts transparent since I got him. As you can see, his fins are tattered and shortened by a lot, but it doesn't seem to be black/white around the edges.

To give some further insight into my tank set up:

- 3-gallon tank (I realize this is pretty small, but he's been absolutely lively and had no issues prior)
- It is a planted tank with a filter, heater (25 C), and 2 zebra snail
- I use Fluval Bug Bites and Omega One Blood Worms, feed once a day.
- His behavior has not changed and he's still nipping, jumping, following me around the room, and eating.
- I tested my water immediately after noticing his fins. I use the API 5 in 1 test strip.
Ammonia: not available on the strip
Nitrite: 0-5 ppm
Nitrate: 0-5 ppm
pH:6.5-7
Hardness (GH): 50mg/L
Alkalinity (KH): 180mg/L

I'm worried as this seemed to happen overnight, or at least very quickly! My water parameters look fine and his behavior has not changed, but his tail looks so tattered and short!! I'm devastated!! Any insight is helpful! Thank you so much!!

 

[Sgooosh]

too much nitrite thats a lot! water chang it out.
your water isnt fine.
what plants do you have he might be rubbing on a hard plant
stress coat may work

 

[eatyourpeas]

What kind of plants are in the tank?
How often do you change the water?

 

[xxamyxx85]

The test strips are not reliable you should really be using the API master test kit, you definitely need to be testing ammonia! Nitrite should be at 0ppm at all times as should the ammonia, aim to keep nitrate as low as possible by performing water changes.

do a water change as soon as possible and test all parameters, i would do daily water changes until his fins have healed. Good luck and I hope he gets better soon.

 

[Sgooosh]

maybe try stress coat too if that is fine for bettas