He's not eating :(

[SharkbaitOHHAHA]

My fairly new Beta fish Sharkbait has not been eating and is getting very weak. I hope somebody helps me...
1. Size of aquarium (# of gallons): 5
2. Is your aquarium setup freshwater or brackish water? freshwater
3. How long the aquarium has been set up? 2 weeks
4. What fish and how many are in the aquarium (species are important to know) Just the Beta
5. Are there live plants in the aquarium? No
6. What temperature is the tank water currently? About 25
7. What make/model filter are you using? No filter.
8. Are you using a CO2 unit? No
9. Does your aquarium receive natural sunlight at any given part of the day? Not too much, but he gets a decent amount
10. When did you perform your last water exchange, and how much water was changed? About 3 days go, 3/4 of it was changed
11. How often do you perform water changes? Once a week
12. How often and what foods do you feed your fish? Twice a day, Wardley Essentials Beta Food
13. What type of lighting are you using and how long is it kept on? A small dim light, it's on for most of the day
14. What specific concerns bring you here at this time? Sharkbait is not eating. He hides in his little cave all day...He hardly comes up for air. He is very slow moving and getting very skinny. I am very concerned :(
15. What are your water parameters? Test your pH, ammonia, nitrite and nitrate. N/A
16. What test kit are you using and is it liquid or test strips? N/A
17. When was the last time you bought a fish and how did they behave while in the pet store tank? My fish before Sharkbait was about a year ago..he lived for about 6 months...I don't want Shakrbait to have the same future :(

[Curegirl80]

Do you have a heater? If the temp is too low, they get a little lethargic.

My betta had protozoan parasites and he was acting the same way: not eating, barely swimming and started getting super thin. As soon as I bought his meds, he has started swimming more, started eating, and looks like he is going to make it.

I hope Sharkbait makes it.