Did the eye bulge out.
It could be the flying foxes. How big are they.
You need to issolate the sick fish and use some melafix to stop infection.
Flying Fox
Info taken from here.
http/www.aquatic-gardeners.org/cyprinid.html
Flying Fox, Epalzeorhynchus kalopterus (Bleeker, 1850)
The Flying Fox is the most colorful of this fish group. For this reason, it has gained popularity in the U.S. over Crossocheilus siamensis and "false siamensis". It comes from the flowing waters of Thailand, Sumatra and Borneo. Wholesalers sometimes deliver this species as Siamese Algae Eater in Finland. This fish is also known as Trunk Barb.
Description: Body and fin shape like two previous species. Thin specimens are often pictured in the aquarium literature. The overall color is warmer brown or even goldish and the black horizontal stripe goes from nose to the fork of the tail like on Siamese Algae Eater, but the part going through the tail fin in darker and broader. There is a narrow golden stripe over the black. Dorsal, anal and pelvic fins have indistinctive dark bands and bright white tips. It has 2 pairs of barbels. Maximum length is reported to be 15 cm (6"). No sexual differences are known.
Behavior: Same as previous species. Adult specimen is territorial and aggressive towards its own kind.
Needs: Ideal pH is near 7, temperature 24-26C (75-79F). It eats all kinds of live, prepared and plant foods. It has not been bred in captivity. Minimum tank size 80 liters (20 gallons).
Compatibility: Flying Fox can be kept in a community tank, but it might chase other fish viciously from its territory. There shouldn't be more than one adult Flying Fox in a tank.