Is one of my fish dying? Should I quarantine him?

Hi there, I have a 40l planted tank. It’s well established, I’ve had the fish (endlers livebearers) just over a year now. I did a water change yesterday and checked parameters and it’s all good. One of the fish is staying at the bottom of the tank and only swims a few cms up before resting on the bottom again. I assume this is a bad sign, is there anything I can do to help him? Should I be quarantining him? Could it be something that starts affecting my other fish? I don’t have a spare tank and won’t be able to get one until Tuesday evening so how would I quarantine him?

I’m sorry, I don’t think he’s gonna make it. His tail looks clamped and it might be infected. If you want to try to save him. I would recommend quarantining him in salted tank, or at the very least doing a water change in your main tank. He may surprise you!

I’ve personally never been able to save a guppy that I’ve found laying on the pebbles and they’ve done so for a variety of reasons: organs falling out of their anus, fin rot, swallowing air, swim bladder disorder, just other infections etc, sometimes I can’t find the reason at all. I typically put them in a QT tank if just so they can die peacefully rather than get nipped by their fellow healthy fish tankmates and cause them more pain. Plus that will help prevent whatever sickness he may have from spreading.

I’ve used spare buckets and large bowls for emergency QT tanks. Slap on a spare filter and a heater if you can and just make sure the bowl is clean with no soap residue. Fill it up with half tank water half clean water and maybe add a decoration or some pebbles to it for the healthy bacteria.