Sick betta

[IHaveAquariums]

So I have 2 bettas in a split 10 gallon tank, one is very aggressive and the other is very passive so passive that I've actually had him in a tank with another male betta before both were amazingly gentle. Each side has a sponge filter and is heated. They also have driftwood and live plants. It has a sungrow heater in it right now but its malfunctioning so it has a tetra preset. Right now my temp is at about 77°. Right now the aggressive one is doing great in his side, nothing going on. My docile one seemed to like having friends so I had 3 platys with him and they got along great. However in the past 2 days, all he's done is lay at the bottom of the tank breathing heavily. I had netted him to pull him up and look at him and his tail looks destroyed. Can't get a picture of it right now but his fins are in bad shape. I took the platys out, nothing changed, he's still laying at the bottom on his side breathing heavily. He doesn't look good and I'm wondering if I need to euthanize him any thoughts or helps would be greatly appreciated!

 

[Angellove78]

Have you tested the water?

 

[IHaveAquariums]

I have not tested the water in this tank however all my tanks are fully cycled and I do weekly 25% changes on this tank. I'll test it to see what it's reading at right now though

 

[IHaveAquariums]

Have you tested the water?

Alright I tested the water, ammonia and nitrite at 0, nitrate 5-10, and pH at 6.8-7

 

[Angellove78]

Maybe your platys started nipping him. The other Betta is fine? Right?? Maybe try feeding him and let him see they are out of the tank. Your water seems good. The other fish are all I can think. If the other Betta is fine something happened in the other side of the tank. The water is filter through the same filter for both side, I'm guessing. Unless there's something in his side that's ripping his tail. ???