Sick Betta Fish - Help Required

[Melj]

I rescued 2 male betta about 3 was ago having seen them in a tiny bowl with a glass separating them and nothing else in their. I have bought a duo 20l tank. The boys have done well and adjusted.
I changed the water on Sunday, used conditioner and they were fine. Since Monday morning now one is fine and happy and the other for the last 3 days spends a lot of time on the bottom of his side of the tank, very lethargic, gulps for air when at surface and refuses to eat. I have searched websites and see it could be 100 different things. The other still happy and eating. No velvet appearance, nor lifted scales. What is the best way to treat this if anyone knows what it is and what do I use? Thanks for your help!

 

[Soccerfreak]

Does your betta flare at all?

 

[NickAu]

Check your water parameters, Ammonia Nitrite Nitrate, What is the water temp? Is the tank filtered? Is the tank cycled?
Can you post a photo of the tank?

Does your betta flare at all?

Why would this matter? I have had males who never flare.

 

[Soccerfreak]

Because if they flare they are stressted which means they will not eat. It happened to my betta.

 

[GobyMaster11276]

I get that your intentions were good, but 10l each is a bit below the recommended 5 gallons. As well as NickAu's questions, what do you feed them and how much of it? Do the fish have hiding spots? Plants? A picture would be great.

 

[DutchMuch]

I think the OP ditched