Fish keeps sinking to bottom of aquarium

[Finn1231]

Hello. My betta obby is about 2 or 3 years old now and has been more sluggish in general but all of a sudden when i went to feed him today he was at the bottom of the tank and every time i tried to bump him with my finger or the net he would swim up a bit before sinking back down. I am very worried and the tank has more vertical area so i put him in my bucket I usually use for water changes and filled it about an inch. It has a few divots at the edges so if he needs more water he can go to the sides. He has really long fins so he’s having a super hard time swimming around and i feel like if i give him much more he will exert himself trying to swim to the top for oxygen. Im keeping the water in the higher 70s-80s because i know hot water has more oxygen and i took the line for His sponge filter out and put it into the bucket to give him more oxygen. Is all of this right? Ill try to pick up some aquarium salts or anything else you guys recommend tomorrow if i have time too. Please tell me, how else can i help him? I think this might have been caused by an ammonia spike and if so he will hopefully feel better soon. He has a 3 gallon aquarium i clean weekly (i know its not often enough) but my mom is thinking about getting me an aquarium rack so i can get him a bigger aquarium. I will get him something shallow but are there any other old fish accommodations?

 

[Fishmanic]

You “think” it may be caused by ammonia. Did you use a test kit to determine nitrates, ammonia, and nitrite levels? Please give us those levels using a test kit such as API test kit.
Was the tank cycled before adding the Betta?
Please post a sideview closeup of your Betta.

 

[Colin_T]

Warm water holds less oxygen than cool water. However, warm water is better for Bettas than cool water, and Bettas can take air from the atmosphere to breath. They do this with the labyrinth organ in their head. They also take oxyegn from the water.

Your best bet would be to leave him in his tank and simply reduce the water level to about 4-6 inches.

The best treatment is a 75% water change and gravel clean the substrate every day for a week. Then do a 75% water change and gravel clean once a week after that. You should also do a 75% water change any day you have an ammonia or nitrite reading above 0ppm, or a nitrate reading above 20ppm.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.

Don't add any chemical medications or salt because they are unlikely to help.