Black edge on silver molly tail

[Tank Mate]

Hi all,

I've noticed a couple of days ago that there is a think black rim around the edge of my male molly's tail. I've had him for 3 weeks and he'd previously been kept by another owner.

My tank parameters are normal, with ammonia and nitrite levels of 0 but I can't be sure of the conditions he was kept in before he arrived.

Behaviour is still normal. He swims up to greet me and is generally a happy and entertaining fish!

Suspecting fin rot but just wanted to check if anyone has any experience with this. Picture attached but will try to get a better one when home.

Thanks in advance!

[Autumnsky]

Maybe a pic of more of the tail section in question? Can't really see it.

[Tank Mate]

Not the clearest, but here it is.

[Autumnsky]

There seem to be clamped fins on the fish in both pics. And that could be some water quality issues to infection. Nice fresh clean water is always important. I would do a couple pwc of around 30% each time. Am and pm pwc or back to back. Just to clean up and freshen the water in the tank.

Rinse the filter gently in treated water. See how it looks. If it's fins seem to stay open and brightens up in color and behavior, then see how it goes for a few days with pwc as needed by test or 2-3 days for a week to couple weeks. I usually try clean water as the first defense. Unless there is a notable reason for medicated treatment.

[Tank Mate]

Thanks for the advice!

Which fins seem to be clamped? There's a gentle flow in the tank that he likes to swim into, and his dorsal fin is rarely raised when he does this.

I did a 20% water change last night and will monitor the changes. I also plan to completely clean out the filter compartment and remove any waste that could be trapped in there. I'll also probably buy some additional biological media just in case!

[Autumnsky]

Betta maybe, Molly seems to be and the Tiger Barbs don't seem to have much fin sticking up in pic, maybe they are younger. Just a word to watch them. Pics are hard to see detail, so you would know better.