Archer Damage, What Is It?

so the skin is exposed and pinkish and protrudes out a bit.

different pic

crap my mono has something strikingly similar too, leads me to think infection and not physical trauma

tank size?
inhabitants?
test results ?

AstonN24vantage said:

tank size?
inhabitants?
test results ?

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parameters good, ammonia, nitrite, nitrate at zill
75g, 4 archers (still small), 3 mono's, 1 dragon goby, 2 orange chromides, 2 spiney eels (small), 2 mollies, purple spotted gungeon, 2 knight gobies, 2 florida flag fish, 1 golden wonder killi, and one horse faced loach.

nothing could really pic on the archers but they could have run into stacked lava rocks, that would be the least worriesome reason.
the tank was at 1.002sg for a 2-3 weeks, but i did a water change a week ago back to 1.005sg
water hardness im not sure of but its very hard with finely crushed argonite sand substrate and a ph of 8.2