Fin and scale damage on betta

We just transferred my daughter's betta from a small 1gallon bowl to a 3gallon tank. He had some plants and a hideaway in the bowl, and somehow must have damaged his back fin and scales in that area.

I checked the hideaway and it's not sharp but it's plausible it was too low before, however isn't now.

Will this heal? I feel so bad. He's hardly lifting them so I think they're badly damaged

 

What are his water parameters? how long do you have him? He nearly looks a bit clamped to me, but that maybe just the picture.

 

What are his water parameters? how long do you have him? He nearly looks a bit clamped to me, but that maybe just the picture.

Not sure what you mean by clamped... his back fin is destroyed and he cannot lift it because I don't think much is left.
He came to us in a 0.7gal tank and belonged to my daughter's stepbrother so I'm unsure how old it is but we have had it for about 3 months now.

He JUST moved from the cramped 1 gallon to the 3 gallon today. Water is reading well across the board and I added some salt to help with the transition as well as all the original tank water and stress treatment.

This is the new set up. The purple plant in the front has alot of free space beind it.

I think he got stuck in his bowl and wiggled loose damaging his fin that way.
Better photo of the damage as well.

 

Sorry...welcome to Fishlore. It is hard from the picture to tell details. Clamped means that the fish keeps the fins close together, does not unfold.
Can you yell a bit more detail what happened and may be fill the Emergency Template?
There are questions in regards to nitrogen cycle, water parameters and other detail important to provide a solution to the problem.

 

Sorry...welcome to Fishlore. It is hard from the picture to tell details. Clamped means that the fish keeps the fins close together, does not unfold.
Can you yell a bit more detail what happened and may be fill the Emergency Template?
There are questions in regards to nitrogen cycle, water parameters and other detail important to provide a solution to the problem.

Tank
What is the water volume of the tank? 3 gal
How long has the tank been running? 1 day with water from previous tank
Does it have a filter? Yes
Does it have a heater? Yes
What is the water temperature? 78 or 79f
What is the entire stocking of this tank? (Please list all fish and inverts.) 1 betta male

Maintenance
How often do you change the water? Generally it depleats before it needs to be changed but we do it 2x a month and as needed
How much of the water do you change? Generally 25% but at most 50%
What do you use to treat your water? Nutrafin Aqua Plus Water Conditioner
Do you vacuum the substrate or just the water? Both. I generally vacuum the substrate, let it settle, then vacuum the settled stuff on top.

*Parameters - Very Important
Did you cycle your tank before adding fish? Yes. Either with a filter I have shoved in the back of my main tank filter, or we use Nutrafin Cycle.
What do you use to test the water? tetra test strip
What are your parameters? We need to know the exact numbers, not just “fine” or “safe”.
Ammonia: 0
Nitrite: 0
Nitrate: 0
pH: 6.8

Feeding
How often do you feed your fish? 1x daily
How much do you feed your fish? A tiny pinch of ground up betta flakes (literally just what he will actually eat)
What brand of food do you feed your fish? Bettamin by Tetra
Do you feed frozen or freeze-dried foods? Frozen Brine

Illness & Symptoms
How long have you had this fish? We have had it 3m, it belonged to someone else prior and I can't tell you how old it is
How long ago did you first notice these symptoms? Today when we transfered to the 3 gallon from a 1 gallon bowl which was a bit crowded
In a few words, can you explain the symptoms? Damage to back and fin. Scales appear rubbed away at the spine where the fin is, fin is rubbed raw and ruined. Fish cannot appear to lift that fin as there isn't much left of it. I believe the fish rubbed against something in the cramped bowl.
Have you started any treatment for the illness? No
Was your fish physically ill or injured upon purchase? No
How has its behavior and appearance changed, if at all? Hasn't changed. He seems fine otherwise.

Explain your emergency situation in detail. (Please give a clear explanation of what is going on, include details from the beginning of the illness leading up to now)

No illness. Fish was moved from a cramped 1 gallon tank with a hideaway and artificial plants and likely damaged his back fin and accompanying scales on decor in the bowl (prior to his transfer).

 

I am new to fish keeping, but I am not really a fan of medications, other members with more experience may chime in.
Bettas are amazingly hardy. My first steps to any issues are daily 50% WC with temperature adjusted water, keep water as pristine as possible and keep the danger of infection low, add an Indian Almond Leaf for added tannins, and keep the lights at a low level. Is he eating?

 

I am new to fish keeping, but I am not really a fan of medications, other members with more experience may chime in.
Bettas are amazingly hardy. My first steps to any issues are daily 50% WC with temperature adjusted water, keep water as pristine as possible and keep the danger of infection low, add an Indian Almond Leaf for added tannins, and keep the lights at a low level. Is he eating?

Yes he's otherwise happy, enjoying all his new room

 

The only way he will heal without complications is if you keep his water clean and cycle the tank properly. Unfortunately changing the water twice per month is not even close to sufficient in a tank that size since toxic compounds accumulate quickly due to the small volume of water. His clamped fins are indicative of poor water quality and stress. I would recommend no less than 2 WCs per week of at least 50% for a tank that small. During the healing process and fish-in cycling process you will likely have to do even more frequent water changes (every 2-3 days) to keep the water pristine as to avoid infection.

Imo the hideout seems like it might have been the cause of his injury. Bettas love to try to squeeze into tiny spaces for whatever reason so he could have gotten stuck and scrapped off some scales. I've helped my fish heal from injuries after he's scrapped off scales on sharp decor and ime the best medicine is clean water.