Goldfish bruised? Help!

[New2fish.]

I've got a black Moore goldfish, which has turned solid gold, but what's wrong with him is I think he's got a bruise on his face and eye. But I don't know if fish can bruise.
It looks like a straight red line from eye to mouth at a slant but it has a grey almost fuzzy or matte layer over it and a little black spot at his top fin.
But he's acting totally normal
He's in a 3 gallon bowl with a filter, aqueon quiet flow internal
He's by himself
With his back fin he's a good 3 1/2 inches
I've had him for 4 months, 3 in a 1gallon bowl with filter and heater, then 1 month in this new tank
I completely clean his bowl once a week, take everything out and clean it gravel included
But I change his water almost 50% 3 time a week. I know he's in a too small of a bowl, but I'm not allowed anything larger.
I feed him Mega one Freshwater fish flakes and API algae rounds
The only thing new is his tank and this cave. Which is plastic but looks like natural flat rocks kinda stacked

 

[SaraB]

It looks like a fungal infection. This is going to sound weird but you may be cleaning too much. 50% of the water is fine but don't take the decorations/gravel out of the tank to scrub. What you are doing is destroying any beneficial bacteria that has built up in the tank. You need that to keep your bowl from constantly cycling. Goldfish also don't need a heater.

 

[King Fisher]

If I had to guess I'd say it's mouth rot. You'll need a fungal medication and probably a bacterial med. Pretty soon too as it's spreading to his eye.

I won't blast you on here but a fish bowl your size for a goldfish isn't a great idea and is probably responsible for the problem.

I'd medicate and try to fix him then sell him or donate him to a fish shop.