Betta's dorsal fin disappeared after three days

[pythona]

I'm really worried about my Betta and I desperately need some advice. I've only had him for three days and I'm not sure what's wrong or how to help him.

Housing:
My tank is 5.3 gallons (24 litres) and it doesn't have a filter, but it does have a heater set to 79. There's no air stone or aeration. I'm keeping him alone in the tank for now.

Food:
I've been trying to feed him King British/Love Fish pellets, but he hasn't eaten anything since I brought him home.

Maintenance:
I've only had him for a few days, so I haven't changed the water yet. I've been using Love Fish Tap Safe conditioner.

Water Parameters:
The ammonia level is 0, but I don't know the nitrite or nitrate levels. The pH is 6.5, and I'm not sure about the hardness or alkalinity.

Symptoms and Treatment:
I first noticed something was wrong 24 hours ago. At first, I thought his dorsal fin just looked a bit torn, but my parents said he always looked like that, so I just kept an eye on him. Now his dorsal fin is almost gone, the colors on his tail are fading, the base of his fin is turning white, and he has a small white lump on his chin. All of this happened in less than 12 hours.

He was really inactive yesterday, but today he's been more active. He still hasn't eaten anything since I got him. I haven't started treating him for anything yet. I'm not sure if he was ill when I bought him, but the pet shop guy said he was a crowntail and that's why his fin looked different. Now I'm worried it was actually fin rot.

[novafx]

It's likely fin rot, which is pretty common in bettas. You've got a couple of options - you could try to exchange him at the LFS, or attempt to treat it with medication and regular water changes, just be sure to follow the instructions on the meds.

[trollmaster]

If you can get your hands on a full test kit, that would be a huge help. Proper betta food would also make a big difference. But for now, just keep doing 50% water changes every two days, that should be enough. I wouldn't recommend taking your betta back to the pet store, to be honest, it'll probably just end up dying quickly.

Also, is your tank planted, and what kind of decor do you have in there?

[starluna]

I think Sean's on the right track, getting those test results would be super helpful. For now, ammonia's the priority, but nitrate and nitrite readings would be great too. You mentioned not having a filter - did you cycle the tank before adding your Betta? As Sean said, keep doing those water changes. It does look like fin rot, which is usually down to poor water conditions. But the good news is it's really treatable.

[trollmaster]

I've gotta say, I'm with Nick on this one - pet shop staff often don't know their stuff.

[earthie_9]

I've always been a bit wary of long-finned bettas, they seem way more prone to finrot. The others have covered the basics - water changes are a must, and you'll probably need to add some antifungal meds to the mix. I'd also recommend looking into getting a small filter, and brushing up on the Nitrogen cycle - it's always a factor when fish get sick.

I'm inclined to blame the petstore for not taking proper care of the bettas - ammonia and nitrites were probably through the roof in those tiny cups. When finrot gets bad, it can deteriorate fins in a matter of days. I lost my first betta to something similar, and at this point, I don't think simple water changes will cut it - you'll likely need to get some meds.

Edit: That betta's not a crowntail, looks more like a halfmoon or delta to me.