Fish stopped eating

Housing:
How many gallons is your tank?
.5 gal. I've been meaning to get a bigger one since my fish as grown since I've gotten him, but now that he's sick, I read to keep him in a half gallon tank anyways for treatment.

Does it have a filter?
No

Does it have a heater?
No.

What temperature is your tank?
I don't know, but the room has stayed in the upper 70s to low 80s.

Does your tank have an air stone or other type of aeration?
No.

Does your Betta have tank mates? What kind?
No.

Food:
What food brand do you use?
Omega one

Do you feed flakes or pellets?
Pellets.


How often do you feed your Betta? How much?
4-5 a day, often split between two meals. I try to fast him once a week.

Maintenance:
Before your Betta became ill how often did you perform a water change?
What percentage of water did you change?
%100 once a week.

Do you vacuum the substrate or just dip out water?
I pour it all out and run water onto the rocks to shake them around in several times to get out any debris.

What additives do you use?
BettaSafe water conditioner

Water Parameters:
I don't know where to find test strips.

Symptoms and Treatment:
When did you first notice the symptoms?
I'm a college student and bring my fish with me to school and back home on breaks. It's about a three hour car ride. He's never had an issue with the trips and water/environment changes before, but this time, once I put him back in his tank at school after break, he stopped eating and hasn't eaten since. That was last Sunday.
How has your Betta’s appearance changed?
His fins kinda look tattered and less vibrant. They'd seemed kinda tattered for months now after a close call with a cat, but that was several months ago and he didn't have any other issues at the time, and I didn't notice anything worsening until recently.

How has your Betta’s behavior changed?
He hangs out at either the top or bottom of the tank, but swims around occasionally and reacts to his environment. he also no longer makes bubble nests.

Is your Betta still eating?
Nope. That's the main issue.

Have you started treating your Betta? If so, how?
So far I've started using aquarium salt yesterday, slowly adding salt diluted in water into the tank, giving him time to acclimate until I reached about half of a teaspoon. I tried giving him part of a pea in case it was constipation, and that was the first thing he's taken a bite of all week, but he spit it back out. He also was uninterested in the new freeze-dried blood worms I got him in hopes to get him to eat. I still put in a pellet at a time in case he decides to eat, but take it out and replace it with a fresh one in the morning and before bed. I also took out all of the plastic plants in case those were causing damage and have been cleaning the tank every 1-2 days.

Also, I don't know if this is anything of importance, but when I moved him back into his tank back on Sunday, he was in the middle of pooping and I didn't realize until afterwards. I think I fasted him the day before for travels, so technically, he hasn't eaten since at least Friday or Saturday.

Does your Betta have any history of being ill?
Nope. He's been a real strong fish. He's survived a cat attack and room in the 50s when my building refused to turn the heat on in autumn and has always been ready to eat.

How long have you owned your Betta? Was he or she a rescue?
I got him last July from Walmart. He seemed as like a normal depressed Walmart betta in a cup at the time and quickly perked up after being brought home and put in a tank.

PLEASE PROVIDE CLEAR PHOTOS
Ezio has always been pale with red fins. His teal accents fluctuate. He seems less vibrant now though. He's a crowntail. Pictures are attached. The water level is lowered because I just poured some water into a cup in preparation for cleaning his tank again.