Sick Betta (pic)

[nicolanicola]

I have a 63 litre cycled tank. My betta has been fine until yesterday. He had initially flared up at my platties when I first got him but calmed down.

Yesterday I added a female fighter, 5 tetras and 2 dwarf Gouramis. Immediately he started chasing and flaring at all the new fish, but especially the Gouramis. I went to my boyfriends and when I came back today, I had a dead molly and a dead female guppy. He has never bothered either of these before, so I don't know if they maybe died from something else. Anyway, all today I have noticed he is still chasing the gouramis. Then a few hours ago, I noticed him hovering at the top of the tank beside the filter. When I looked closely at him, a lot of his fins have become threadbare, you can only see the the thread running through them. He was not like this yesterday. I have not seen any other fish bothering him,it's been the opposite. What do you think is wrong with him? Is it stress? I have tested the water, there is no ammonia or nitrite and minimal nitrate.

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