Reticulated Hillstream Loach White Patch

[hillstream86]

The issue:
Last week, I noticed there are some white patches on the sides of my reticulated hillstream loach(female) in the display tank. There are a total of 4 white patches: 2 left + 2 right, all located on where her pectoral fins meet her body. The picture is taken from the right side where the largest patch is. These patches are not very easily identifiable, they are not fuzzy or hairy so I'm hesitant to say it is related to fungus. I observed the patch for 3-4 days and there was not developments.

However, since I was unable to identify the issue and worried it might infect other fish, I rehomed her to a 10 gallon bare bottom hospital tank with some fake decors. Here is a picture in the hospital tank: https://imgur.com/a/k81lxj8

Display Tank Setup:
I got my reticulated hillstream loach 4 months ago from a LFS and it has been in the 75 gallon with 1 anglefish, 10 cardinal tetra, 5 peppered cory, 6 glowlight tetra. It seems to be healthy and happy, scrapping the algae on the acrylic tank and on the stones(mostly seiryu stones).
The tank is cycled with 0 ammonia, 0 nitrite, 5-10 nitrate, 7.8 PH, KH 9 dKH, GH 5 dKH, temperature 76-78 F.
The plants are 3 amazon swords, 5 anubias, 8 java ferns.
Substrates are mostly fine sand in the foreground(50%), and slightly coarse sand(0.5-2.0 mm grain-size)
Filtration: FX4. (with 75% of full capacity)
Water change: weekly 20% water change. The bioload is very low for now(Nitrate below 10).


Other observations:
Eating: I never seem her eating the food I put into the 75 gallon tank: Hikari algae wafer, repashy green gel, frozen blood worms, Xtreme bottom wafers, Xtreme nano sinking pellet and other food sinks to the bottom. 99% of time I see her is grazing on the wall/stones.
Growth: I hear hillstream loach is a slow grower. I do not observe significant growth in the past 4 months. She came in around 2 inches, now she's maybe 2.1-2.2 inches. Too hard to tell since I didn't get the exact measurement when I fist got her.
Activity level: I'd say not too active not too shy. She spends most of the time on different rocks. When the lights are out or no one is observing her in the fish room, she tends to hang on the wall grazing algae. The activity level does not change after I notice the white patch issue. She ignores tankmates most of the time but will chase away pepper corys when they get too close.
Other tank mates: All others are doing good, responding to food actively and no signs of stress/disease.

Should I worried about the white patch on my hillstream loach? I'd be super grateful if anyone has a clue on what might be. Any suggestions are sincerely appreciated!