protozoan · freshwater

Hexamita (Hole-In-The-Head Parasite)

Hexamita is an internal protozoan parasite that causes white stringy feces, weight loss, and the classic "hole in the head" disease in cichlids. Treatment: metronidazole.

Severity: Moderate - treatable if caught early

Symptoms

White stringy feces
Weight loss despite eating
Holes/pits along lateral line + head
Loss of appetite
Bloating

Cause

Hexamita parasite enters via contaminated food or stress. Most common in cichlids (oscars, severums, discus, angelfish).

Treatment

Always treat in a separate quarantine tank. Most medications are toxic to coral, invertebrates, and live rock biology.

Metronidazole (Metroplex). Most effective treatment. Dose per Seachem instructions for 7-10 days. Mix with food for internal infection.

API General Cure. Praziquantel + metronidazole combo. 7-day course.

Improved diet + vitamins. Soak food in Selcon vitamins. Reduces susceptibility.

Prevention

Pristine water, varied vitamin-rich diet, reduce activated carbon (depletes vitamins).

Browse the full disease database for 45 aquarium conditions with treatment protocols, or check the care library for prevention-focused husbandry guides. Use our symptom matcher to rank likely diseases from observed signs, the water parameter checker to diagnose related water-quality issues, or the QT timeline calculator to plan a treatment schedule.

Aquarium-keeping fundamentals

Whatever specific topic brought you here, four fundamentals govern long-term aquarium success: water quality, parameter stability, biological filtration, and species-appropriate husbandry. Skip any one and the others struggle to compensate.

Water quality: ammonia + nitrite at zero, nitrate under 30 ppm freshwater + 10 ppm reef. Test weekly with API or Salifert kits. Use our water parameter checker to score your readings against your tank type.

Parameter stability: stable wrong parameters beat fluctuating ideal parameters. Most fish tolerate a wide pH range if it's stable. Sudden swings of 0.4+ pH or 5+°F kill fish faster than chronic suboptimal values. Use temperature controllers (Inkbird) + automated dosing for consistency.

Biological filtration: the bacterial colony on your filter media + rock + substrate is the engine. Never replace all media at once. Use our filter turnover calculator to size correctly.

Species-appropriate husbandry: research adult size, territoriality, diet, and tankmate compatibility before purchase. Use our tank stocking calculator + compatibility guides.

Frequently asked questions

How long does an aquarium take to set up? 4-6 weeks for full cycling + first stocking. Use our cycle ETA calculator + how long does cycling take.

What's the best aquarium for beginners? 20-gallon long. Big enough for parameter stability, small enough for budget + space. See beginner picks.

How often should I do water changes? 25-30% weekly. See water change frequency Q&A + water change calculator.

Why does my fish keep dying? 5 leading causes: uncycled tank, wrong species pairings, no quarantine, undersized tank, neglected water-change schedule. See full diagnosis.