a betta with a white spot

[helptoall]

Hi yesterday ive noticed a white spot appeared on a beta ive rescued 2 weeks ago . It dosent seems buldging, and its kinda like a V shaped white scratch.
The thing is theres nothing in the tank to scratch him so its kinda weired. its really hard to see but here are some pics, ant ideas what is it?
thank you

Btw the bucket is a 20l with no filter cuz he was almost sucked in when i tried to put one and an air stone, water temp is 27 and of course that this is a temp quarantine

 

[Colin_T]

any chance of a picture showing his side with the mark?
and where is the white mark located on his body?

 

[FishGuest5123]

That plastic plant could have scratched him or was that added afterwards?

 

[Essjay]

I agree, plastic plants have sharp edges.

Instead of an air stone, you could attach a sponge filter to the air pump outlet. That's what I have in my betta's tank.

 

[helptoall]

thanks for the responses, the white mark is on his forhead the pic that ive uploaded is the best i managed to take\
i guess the plastic plant is an option, but is he really powerful enough to swim that fast so the plastic plant will cause it?

 

[Essjay]

Bettas will try to squeeze through the tiniest spaces. If the mark is on his forehead it does suggest trying to squeeze through something that has cut him. Mine will push and push to get through between the floating plants and the glass.

 

[helptoall]

Hi, the spot is gone but 3 days ago he started to show signs of finrot.

its progressing so i want to try and treat with methylene blue. The thing is there are a few diffrent dosage recomandations online. Do you know whats the reccomended dosage for a bath? how much ppm should it be? thank you