Help Rescued/sick Betta

I rescued a betta from getting flushed at petsmarts and idk what’s wrong with him, he floats on his side and can’t swim, hasn’t eaten since I’ve he’s him (4 days) there’s this slimy mucus in the water, heavy breathing and one eye is clouded

 

There is a sick fish template on the forum somewhere, if you fill that in with all the information then people might be able to help you easier.

ETA: Sick fish template link
Fish Emergency Template

 

First things first- have you been changing his water? Your profile says you don't know the nitrogen cycle so definitely look into that.

If he is floating on his side and can't swim then he has swim bladder disorder. The mucus may be fungus or algae.

 

First things first- have you been changing his water? Your profile says you don't know the nitrogen cycle so definitely look into that.

If he is floating on his side and can't swim then he has swim bladder disorder. The mucus may be fungus or algae.

I’ve been doing a 50% water change every other day the tank I have him in doesn’t have a filter (it’s just a temp

 

Add Indian Almond Leaves to his tank... Tannings released by these leaves are beneficial and create a natural environment for your betta. Also helps in finrot recovery.
A sponge filter is also better. Do take care not create too much flow as he having trouble swimming.
Go though this link for swim bladder disorder