can we please get a little background--if you can answer as many of these questions as possible it will help us figure out what this is.
what size is your tank? Divided 5.5 gallon
what temperature is your tank? 79 F
does your tank have a filter? No
does your tank have an air stone or other type of aeration? No
is your tank heated? Yes
what tank mates does your betta fish live with?
what type of food do you feed your betta fish? New life spectrum small fish with occasional brine shrimp.
How often do you feed your betta fish? 2-3 times daily
how often do you perform a water change? Weekly
what percentage of the water do you change when you perform a water change? 50% to 100%
what type of additives do you add to the water when you perform a water change? Prime
Have you tested your water? If so, what are the following parameters?
Symptoms and treatment
how has your betta fish's appearance changed? His pectoral fin turned purple. Now it seems to have ripped. I will insert more pictures below.
How has your betta fish's behavior changed? He seems to be acting normal. Swimming and eating fine.
When did you start noticing the symptoms? Yesterday i noticed he was not using his fin and today i saw his fin purple.
Have you started treating your fish? If so, how?
Does your fish have any history of being ill?
How old is your fish (approximately)? I don't know.
Is he eating? Yes
is his activity level normal or if it has changed how so?
You say he wasn't using his fin--can you describe his swimming in a little more detail?
He had it tucked to his side but was swimming normal otherwise.
What is in the tank with him decoration wise? He has silk plants, Eiffel tower decor and a hammock made of mesh.
Anything else you can tell us will help.