A plastic peanut butter jar for a Betta

My Betta lives in a reg/large size plastic peanut butter jar. Despite that, he's five years old and just seemingly start to have problems. Should I change the jar?

And how is ammonia poisoning created?

Because he has kind of reddish gills now should I change the water everyday now for a change?

He also has this small gole in his pectoral fin(the front fin)

Someone suggested PimaFix. But does Betta Water Conditioner work like PimaFix? Two years ago, I used Betta Water Conditioner when his tail got this hole too and he healed.

I would say, yes, change the jar or change the water in the jar. I wouldn't recommend anything less than a 2.5 gallon filtered tank for Bettas. They sell these tanks cheap at PetSmart (Under $10.00). You can buy a 2.5 gallon kit (Top Aqua Scene 2 for $9.99) or get a standard rectangular 2.5 gallon aquarium and buy the filter, air pump, substrate, and a silk plant . After buying everything- you'll be out $30-$40 tops. Make sure you read up on tank cycling prior to adding the Betta to a new tank and that will give you more insight into ammonia and nitrate levels. You may want to keep the Betta in a cleaner jar until the tank has sufficiently cycled.

Ammonia levels are caused by waste from the Betta and excess food in the jar. In a peanut butter size jar, you'd have to conduct a water change every few days to keep the ammonia level under control.

The redness on his gills is most likely caused by by irritation from high ammonia levels (or high chlorine levels if his water is untreated). His gills are essentially "burning" from the ammonia. He may also flare his gills more often in order to sooth the burn. If he had more room he would be swimming rapidly or "darting" to also help cool the burning. If you haven't already, change the water now! Use a Betta Conditioner to remove any heavy metals, chloramine and chlorine from any water you add to the jar.