HLLE causes pitting erosion of skin around the head and lateral line of marine tangs and angelfish (especially powder blues, hippos, blue tangs). Cause is debated: nutritional deficiency (vitamins A, C, D), low electrolytes, stray voltage, or activated carbon.
Less common in freshwater. When seen, vitamin supplementation + improved diet typically reverses.
Improve diet: feed nori, frozen mysis enriched with Selcon + vitamin C, vitamin-rich pellets like Sera Marin Gran Carbon. Reduce activated carbon use (some studies link it to HLLE). Add stray voltage check - install a grounding probe to drain any electrical leakage. Check for low alkalinity / low magnesium - both contribute. Resolution takes 3-6 months of consistent treatment.
Vitamin-enriched diet from day one. Run carbon only as needed (not continuously). Install a grounding probe. Stable alkalinity + magnesium. Avoid chronic stress (aggression, parameter swings, overstocking).
Estimated cost: $40-80.
Usually yes if caught early. Dietary improvement + parameter stability + grounding probe addresses the contributing factors. Reversal takes 3-6 months. Severe long-standing cases may have permanent texture changes.
The link is correlation not proven causation. Some long-term studies suggest carbon-tank fish develop HLLE more often than no-carbon-tank fish. Practical recommendation: run carbon as-needed (every 4-6 weeks for 1-2 weeks), not continuously.
The single most important disease-prevention step: a 4-6 week quarantine of every new fish before adding to your display. See the complete quarantine protocol.