Marine Ich
Symptoms
Tiny white spots on the body and fins — slightly larger and rounder than freshwater Ich. Heavy infestations show breathing distress as gills are colonized. Flashing against rock and substrate. Discolored patches, ragged fins. Most virulent on tangs, angels, butterflies — but no marine fish is immune. Mortality is high if untreated.
Causes
A ciliated protozoan with a four-stage life cycle similar to but distinct from freshwater Ich: trophont (feeding on fish), protomont (drops off), tomont (substrate cyst, can take 28-72 days at typical reef temperatures), theront (free-swimming, infects new hosts). The long cyst stage is why marine Ich is so much harder to eliminate than freshwater — you cannot treat your way out of it in 14 days.
Treatment
Copper sulfate at 2.0 ppm therapeutic level (test with a copper meter — under-dosing fails, over-dosing kills) for 30 days minimum in a hospital tank. Alternatives: chloroquine phosphate or tank transfer method (move fish between bare tanks every 72 hours for 12 days, breaking the life cycle). Copper KILLS all invertebrates, corals, and live rock biofiltration — never copper a reef tank. Display tank must run fishless at 78-80°F for 76+ days for the parasite to die off without hosts.
Prevention
Quarantine EVERY new fish in a copper- or chloroquine-treated tank for 30+ days before adding to display. Do not skip QT. Marine Ich is the single most preventable mass die-off in reefkeeping and the single most common reason new reefers lose their stock. There is no shortcut.
Notes
Garlic, herbal 'reef-safe' remedies, and UV sterilization do not cure Marine Ich — at best they reduce visible symptoms while the parasite persists. Reef-safe treatment doesn't exist; the only options are quarantine + treat, or stay fallow. Plan QT into your stocking timeline.