Here read this.
HLLE is not a contagious fish disease but, rather, a condition where the epidermis and scales along the lateral line and face of the effected fish become pitted and eroded. HLLE is thought to result in captive fish subjected to poor environment, poor nutrition, poor care and sometimes even another disease process. There is not always an obvious “cause” because many hobbyists may have what is considered a good setup with even so-called “pristine” water quality, but still have developing HLLE on a fish. If the cause of HLLE is not adequately addressed the smaller pits observed at the onset of the condition will enlarge and spread and could end up covering much of the fish’s body.
There are several ways to address HLLE:
Grounding Probe
All marine tanks must have grounding probes installed in each system: the tank, the sump, the refugium, etc. The grounding probe must be installed along with a properly installed Ground Fault Circuit Interrupter (GFCI) where tank electrical equipment is plugged in. There is no “ifs or buts” about this. Grounding probes are necessary to prevent the electrocution of hobbyists.
But what does it do for fish and the prevention of HLLE? Debatable is the answer.
The long-standing hobbyist theory
Grounding probes should be installed in all tanks and supporting systems [sumps, refugium] due to stray voltage in the aquaria caused by electrical equipment used in and near tank water [powerheads, lighting, heaters, filters, etc.]. Stray voltage is a causation of HLLE in sensitive fish such as tangs and angelfish; the irritating nature of this stray voltage results in the erosion of the lateral lines of fish. Properly installed [grounded] grounding probes in conjunction with a GFCI will divert or eliminate stray voltage out of the tank, thereby reducing or eliminating the cause of HLLE.
There is considerable anecdotal evidence to support this hobby theory.
The alternative-perspective
Grounding probes complete the circuit for electricity to flow, therefore causes more of a hazard to marine animals.
Explanation
Tank equipment is connected to a properly grounded GFCI with a grounding probe installed in the tank. A minute amount of voltage occurs due to tank water contact with an electrically defective pump, heater, etc. This small amount of voltage passes through the grounding probe and IS NOT detected by the GFCI because the voltage is very low. Because this voltage goes undetected by the accompanying GFCI, AND the grounding probe provides a grounded source of current, the tank is now charged with minute amounts of electricity that poses a thread to marine life. If a grounding probe was not installed, there would be no “current” by which electricity could travel, therefore, no threat to marine life.
Grounding Probe Essential for Hobbyist Safety
The grounding probe connected to a grounded GFCI will allow current to flow through the water providing the path of least resistant which is through the probe [and not human hands, or arms]. Bottom line, grounding probes are for human safety, not fish safety.
Human safety must always be a priority, therefore grounding probes must be installed in the aquaria.
My Yellow Tang was also loosing it's color and turning white.