[sayurasem]

so I have my tetra for quite a while. first time happening to me, my tetra's mouth are deforming over time. each day their mouth is turning white-ish and starting to swollen/ deforming. some cant even move their mouth because its open/hardened.

is it because too much co2 in my tank?

help pls.

 

[Higher Thinking]

Doesn't sound like anything to do with CO2, but rather a bacterial or fungal infection of some sort. Put up a picture if you can get it. Most likely you will need to medicate with something.

 

[CaliEAB]

It's not co2. Too much co2 makes fish gasp at the surface and reddens their gills. Infection of some kind. Post a pic.