Zebra Danio having difficulting swiming

[Smilecentaur]

This seemed to have recently started and im not quite sure what the cause is. He seems to be still fairly active but he's swimming by like wiggling and keeps flipping upside down. His fins are all intact so I know that's not the issue. I'm not sure whats going on or how serious this is so any help would be appreciated. He is in a planted tank 20 gallon with 4 other danios and a female betta. The other fish seem fine. It just looks like he is affected.

 

[Metalhead88]

How long has the tank been set up?

What are ammonia, nitrite, and nitrate levels?

What size tank?

How often do you water change and much do you take out?

Sadly, when a fish is swimming like this, he is likely on his last leg. It can be caused by a number of things, but if you answer these questions we can try to make sure this doesn't happen to the other fish.

 

[Smilecentaur]

The tank has been set up for well over a year now. It is a 20 gallon. I do a water change around once a month and change about half the tank water.
Ph-6.8
Ammonia- 0ppm
nitrite- 0ppm
Nitrate- 0ppm
He doesn't act as if he is on his last leg, just as if he can't keep himself upright. He is not lethargic and still as active as all the other danios. I would post a video but it doesn't look like I can.
Thank you for your help.

 

[LostBear]

I'm having a similar problem with my glowlight tetras.

Seemed fit and healthy then suddenly - pouff! Apparent swim bladder problems.

I'll be interested to see if anyone suggests anything for you. (I've also got a thread - not hijacking yours, but hopefully we'll see some traffic that will help us both)