Pop Eye Or Did He Just Get A Beating?

I have a 30 gallon aquarium with a harem of bettas (3 females and a male), an algae eater and a school of 10 neon tetras.
Today I noticed my male Betta acting weird. Is this pop eye, or did he get a beating from the girls? Will he be fine?
They've been getting along just fine for the past 3 months. However, two days ago I added a new female, after the previous one passed away.

 

It resembles more like a beating. Also the patch seema darkened and swollen.
In case if it was pop eye it should occur on the topside of the eye and not the front.
So keep a tab on how the new female behaves with your male.

 

Will he be fine? Can I let him back into the tank, or should I set up the quarantine tank? I've tested the water for ammonia and nitrates, nitrates show 15 and ammonia shows 0.
He seems to have trouble breathing through his gils. Always stays near the surface of the water and takes gasps of oxygen from the air instead.

 

I set him ip a quarantine tank. He's resting on top of a plastic castle I gave him, but keeps swimming up for air. Will he be alright? I'm really worried.

 

He's currently staying next to the filter with his head down and tail straight up. Can I help him anyhow?

 

#1. How old is he.
#2. My betta always goes to surface to gulp air, every two minutes. And he is doing awesome and so are the water parameters. So relax about that.
#3. You can reduce the water height (or increase castle height) so that he can rest on castle and easily breath air.
#4. About his being near filter: I have seen many post of bettas doing that so I will not worry about it. Just keep a tab on how much you feed him, or you will overfeed and cause bloating. Also reduce the output flow of filter if possible.
#5. If possible add IAT leaves (catappa leaves to tank). Its medicinal for your precious betta, and boost their immune system.

Keep us updated.
Wish a fast recovery for oir precious pet.