Why is my guppy fish floating? He is not as "bloated looking" like the...

...other guppy though.? I have a 20 gal tank. Fish has been floating right side up for 1 month but it started floating upside down now.
I changed 25% of the water twice, 4 days apart and added Fungus clear tank buddies in with each change. I tried adding one table spoon of salt today with no luck. I have heard of feeding a cooked pea without the skin to help with bloating and cure it, but it doesn't look as bloated as the other healthy guppy that i have so i didn't feed it the pea. Is the pea remedy going to help or is there another way?
 
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