Whitish film on body of ocellaris clownfish

Yesterday I noticed a slight white film on both sides of my male clownfish as you can see here:

Picture's not the best and I'll try to get a better one if I can get a shot at him.

Tank parameters are:
Ammonia: 0
NO2: 0
NO3: 0
pH: 7.0-7.5
Salt: 1.020ppm

I've had these fish for about 4-5 years now and nothing has been added to the tank in about 6-12 months.

Some background info:

1. A few weeks ago I noticed that he was starting to hang out on the other side of the tank quite often. I found this kind of strange because for the past 4 years this pair has stayed in the same general area. They've lived in two anemones over the years and are currently inhabiting a large mushroom coral that has sense taken the place of the anemone after a bad accident with the power head mortally wounded the anemone. However, I haven't seen him over there in about a week or two and he's back to living with his lady in the mushroom.

2. I've also noticed that he's swimming straight down and sometimes completely upside down. I'm not sure what this could mean. He's perfectly capable of swimming normally and he does so 90% of the time. Sometimes he'll just nose dive into the coral and stay there upside down. I've noticed this in the past but now he's doing it a lot more often.

3. I haven't noticed any loss of appetite yet either. He'll eat with the others but not as much as the female clown.

4. The marking/film is about the same size and area on both sides.

Any ideas? Any suggestions for treatment?

Anyone? Nothing? Not even a suggestion? Anything will be helpful.

My biggest concern was Brooklynella. Though nothing has been added to the tank in about a year like I said. From what I understand brooklynella only happens to new wild caught clowns, not 5 year old tank inhabitants. He hasn't lost his appetite either which I understand is another tell tale sign of brooklynella. Given the quick progression of brooklynella, certainly he'd have died by now. The patch shows no sign of growth and he seems to be acting pretty normal other than the upside down swimming on occasion. So I think I can rule that out. I've been looking around for other infections/illnesses but I can't seem to find any solid information on what this might be. I don't want to put him through the added stress of a freshwater dip and QT if I don't have to.