Help! Sick betta!

[bettasrcool]

i got a betta a while ago, and out it in a 2.5 gallon tank with a divider and another betta. Well, the other betta died randomly, so I cleaned it out really well, got a heater, and put in the remaining one.

Now, it is really skinny, crooked when you look over the top, and not eating pellets anymore, only a few frozen bloodworms. It sits either at the top water line or on the bottom of the tank kinda on its side. I put it in a "quarantine" smaller tank, and really cleaned out the 2.5 gallon.
HELP!

 

[bettasrcool]

He also randomly darts super fast and runs into the sides and bottom of the tank.

 

[rubyfire]

ive herd that the pellet food isnt a very good diet for bettas. meybe it is because of that.

also, you didnt use soap to wash the tank out did u? the soap would most likely stay and pollute the water but if you rinse it out realy good then there shouldnt be any in there.

and the new water for the tank should be left alone for a wile to become room temp or the temp of the heater. when it is room temp or the temp of the heater, slowly get the fish used to the water before putting it in.

hope i helped.

 

[bettasrcool]

I used soap but I was sure to wash it out really well, and i match the temp of the new water to the old water and use betta water conditioner

 

[bettasrcool]

I think it has fin rot cause its fins are alot smaller and you can see the "spikes" in between the webbed parts of his tail

 

[bettasrcool]