You can get lateral line get you some info.
Head & Lateral Line Erosion
Taken from this link.
http
/www.fish-disease.net/diseases.htm
Symptoms:
This disease is marked by open pitted wounds around a fish's head and along the lateral line, as if something is slowly eroding away the flesh. It is very similar to the freshwater disease Hole-In-The-Head. Head & Lateral Line Erosion (HLLE) is not fatal in the short run, but if the disease continues to progress, the fish will stop eating and become lethargic. Furthermore, the open wounds caused by HLLE make the fish susceptible to other infections which in turn leads to the further deterioration of its health. These secondary infections are usually the cause of death.
Cause:
Unknown cause, although it is thought that there may be several contributing causes including stray voltage in the aquarium, poor water quality and environmental conditions, high nitrate levels, lack of vitamins and poor nutrition, stress, parasitic infestation (the protozoan Octomita necatrix), or using carbon. Some fish, like Tangs and Surgeonfish, seem to be genetically predisposed to this disease.
The lateral line aids fish in detecting small microvoltages emmited by prey or predators during muscle contraction. The induced voltages from any submerged coil device such as a powerhead, heater, and pump can all add voltage to the tank. This stray voltage can irritate a fish's lateral line if it's constantly stimulating it and eventually lead to erosion of the skin overlying this structure.
Treatment:
Medications do not seem to do much for this disease, although the use of medicated food is recommended to prevent bacterial secondary infections. The best intervention, however, seems to be improving the water quality and supplementing the fish's diet with vitamins, particularly vitamins A, B, D, and E as well as iodine. This can be done several ways. Food can be soaked in water with a drop of liquid multivitamins, such as Selcon or Zoe. Alternatively, fish could be fed fresh or frozen vegetables, such as broccoli, zuchinni, and peas.
The importance of good regular aquarium maintenance cannot be stressed enough. Eliminate any stress-inducing factors. It might also be a good idea to add a grounding probe to the aquarium if you suspect that there may be stray voltage in the aquarium.
