[Grah the great]

Remove the dying fish to a quarantine tank pronto. He could easily get the other fish ill with whatever is killing him.

By the way, gourami and bettas are known for fighting with each other due to being closely related and viewing each other as competitors. I'm glad it is working for you right now, but keep an eye on that tank in case that changes

 

[Chris_Produces]

I had issues with my dwarf gouramis doing this because I couldn't keep the optimum water conditions. Eventually all but one has passed. Could have been a bacteria but I never knew for sure.

 

[roadmaster]

Iridovirus among this species is common, but it might also help to know what water parameter's are,how long has tank been running with fish.

 

[experz]

Well, the second gourami is fine.
My tank size is 60L, water temperature stand's on 25C.
Air pump is working, and more air from the filter.

No signs of disease, maybe stress...

At the beginning they were together (The Dwarf Gourami's), never saw them fighting.
And somehow they are very playable with my Betta.

About the water parameters like pH, Kh & other, I've got no idea.
I never used them, and my dad's never used them all was fine...
Maybe I'll start to if I'll buy live plants.

He's kinda now more active but in one place, sometimes going up to take air.

I cycled 25% water change 5 days before I bought the Dwarf Gourami's.

Thanks for the quick replay everyone!

 

[stratg5]

What are your water parameters? Dwarf gouramis are pretty hardy. But they will fight if they're both males. One will claim territory and fight to keep the other one off of it so you really should only keep one male in a tank unless you have a large tank with lots of places to hide.