fin rot?

Hi i bought my betta that i call Chad a few months ago allmost 3 months ago (bought him on march 6th)
and he had these fins that i thought were normal to him (hes actualy a veiltail) and i asked around on diffrent forums they thought he just only nipped himself which also made lil holes in it before i had him.
but now he had some new ones and i found out those pins might be fin rot and i bought some melafix and Methylene Blue that will arive soon cuz we dont have it in fish stores here too badly.

is this finrot? and what is the best way to fix it cuz i want him to be happy and not in any pain if it gets worse. How do i treat the melafix to my betta the best way? i have him in a 18 gallon tank with some other fish (all peacefull fish and they all get along) are they able to be in that tank while i put the melafix in to help my betta? and one of his pin holes got bigger and split eventualy the whole tail

It is fin rot.

Do NOT use the melafix, it could kill him. It has oil in it that rests at the surface of the water and when he goes up to breath air it will coat his labyrinth organ and could suffocate him.

Dont use any medication unless it is a last resort and you know the cause of the issue.

What are your ammonia, nitrite and nitrate levels?

What size tank?

How often do you do water changes and how much water do you change each time?

For now do a 75% water change every day for two weeks. You can also dose with aquarium salt.

Then let us know how it went and if he improved and we can reassess.

is the Methylene Blue alright to use if i need it for betta fish? and does the indian almond leave also work to get his health up?

i normally change 25% aquarium water each week or higher and add aquarium conditioner, starter, safe and balance.
i also found a solution to my automatic aquarium filter that i got with the aquarium and also a heater with it (it was streaming too fast so i put a sponge at the end of the ''waterfall'') and the heater isnt doing that great so i bought a diffrent heater (the heater that i 1st had was suppose to do 25/26 celsius (77 78.8) but the aquarium measured 24/25 celsius everytime which is too cold.

size tank: 68liter (17.9 gallon)
results now:
no3- 0
no2- 0
GH- 8d
KH- 6d
PH- 7.2/7.6
Cl2- 0

im doing the 75% water change now everyday but before i did the water change i had some nitrate and nitrite
before the water change i had no3 0-1 and no2-10

the im not sure how much the ammonia is i thought it was on one of the test strips i had but it wasnt so im going to buy a kit for that.

im already seeing changes using the 75% water change!
some holes dissapeared and i think the split fin is healing

he only has 1 tiny hole right now and the split fin and the red brownish colours started to fade/leave on jaged fin edges.