Hard to see the holes in the photo, but at least they are not 'massive' in size.
I think I'd approach it like HLLE. This article has info on that for your consideration:
http://reefkeeping.com/issues/2005-06/sp/index.htm
In order of what I think is most likely:
Vitamin deficiency (A and/or C); Poor Nutrition
Chronic Stress
Poor water quality (including high levels of dissolved organic matter and/or nitrate)
Activated carbon (either removing something the fish need or the dust clogging the pores on the fish)
Stray Voltage (is your system grounded properly?)
Retrovirus
Hexamita
Amyloodinium-like dinoflagallate
Since your experience with the owner is one of poor attention, I'd put emphasis on improving the diet and water quality to the absolute top/best you can.
Only feed brine shrimp that have been gut loaded with spirulina, fats, and vitamins. Keep rotating different brands and differently gut loaded products. Then, only feed brine shrimp no more than once a day or once for every three meals. The other meals should be other foods containing meaty products with a lot of green matter.
If it will eat flake (and many can learn to do this) try to feed it Formula 2 flake. Alternatively, Formula 2 frozen and/or pellets. Soak everything in vitamins once a day and fats once a day and nothing once a day. This means it should get at least 3 medium sized meals a day.
Provide it a bit of seaweed/nori every day, even if it ignores it. (Remove the old and put in new every day). Try a variety of brands and colors (green is most often accepted, but try red and purple, too).
If it will eat gelled food, try that too. The gelled food often traps nutrients in the gel that benefit the fish more than just soaking foods in vitamins. Mine would eat such gel formulas as: VHP, and Angel.
Lastly, once a day give the fish beta glucan in its food (probably that third feeding). Beta glucan is a fine immune stimulator and can be gotten from a (human) health food store.
Still, investigate those other causes and make sure you address each other should there be a combination of problems.
I hope the above has been of some help, guy! :rollface: