Marine Fish Quarantine Protocol: The 6 Week Standard That Prevents Ich and Velvet

Marine fish quarantine is the single practice that separates a stable reef tank from a graveyard. Marine ich and marine velvet, the two parasitic diseases that kill more saltwater fish than every other cause combined, are not preventable in a display tank with rock, sand, and invertebrates. They are only preventable through a 6 week QT protocol in a bare tank with copper or chloroquine phosphate. This guide covers the QT tank setup, the treatment math for each disease, the observation periods, the exit criteria, and the alternative Tank Transfer Method that works without medication.

Why quarantine is non-negotiable

Cryptocaryon irritans (marine ich) and Amyloodinium ocellatum (marine velvet) are obligate parasites that complete their life cycle in saltwater. Both have free-swimming larval stages that find a host fish, attach, mature, drop off, and reproduce. The off-host stage is what causes problems: it persists in rocks, sand, and equipment for weeks. A treated display tank that has had fish removed must sit fishless for 76 days to ensure the parasite cannot find a new host and dies of starvation.

The practical reality: every new marine fish, regardless of source, may carry one of these parasites. Reef-safe medications do not exist. Garlic, vitamin C, and UV sterilizers do not cure these diseases (they reduce load but do not eliminate). The only reliable prevention is QT every fish for 6 weeks before adding it to the display.

The QT tank setup

A quarantine tank is intentionally minimal. The goals: easy water changes, easy observation, and zero porous surfaces that absorb copper.

Required equipment:

• 20 to 40 gallon glass tank: standard rectangular shape, no overflow needed
• Sponge filter (run continuously in the display sump for at least 4 weeks before QT use to seed bacteria) plus a hang-on-back filter
• Heater: 100 to 150 watts
• Thermometer
• Air pump and air stones: copper depletes oxygen, additional airflow is needed
• Mature seasoned PVC pipe sections: 2 to 3 short sections for hiding, sterilized between uses
• Tank-specific tools (net, siphon, scraper): never crossed with display tools
• Test kits: ammonia, nitrite, nitrate, pH, and a copper test (Hanna HI702 Checker for Cupramine, or Salifert copper for general use)
• Lid: marine fish jump

What is NOT in a QT tank: live rock, sand, corals, invertebrates, any porous surface. Plastic plants are acceptable.

The copper protocol

Two main copper products in 2026:

• Seachem Cupramine (ionic copper, the most common): target 0.50 ppm, 14 to 21 days
• Coppersafe by Mardel (chelated copper): target 1.5 to 2.0 ppm, 14 to 21 days

Cupramine is the cleaner option and what most reefers use. Coppersafe is harder to remove from a tank when the treatment ends.

The dosing schedule for Cupramine on a 20 gallon QT:

• Day 1: dose 1 ml Cupramine
• Day 2: dose 1 ml Cupramine
• Day 3: test, should read 0.30 to 0.45 ppm, dose 0.5 ml to bring to 0.50 ppm
• Day 4 onward: test daily, dose to maintain 0.50 ppm
• Day 14: copper has been at therapeutic level for at least 11 days
• Day 14 to 21: continue treatment if fish are still showing signs
• Day 21: remove copper by adding fresh saltwater changes (25 percent every other day) until copper reads under 0.05 ppm

For velvet, target 0.55 to 0.60 ppm for the full 21 days.

Side effects of copper: copper stresses fish. Watch for reduced appetite (most fish go off food for 2 to 4 days after starting copper), heavy breathing, and clamped fins. Wrasses, mandarins, and angelfish are particularly copper-sensitive. Tangs, clowns, and damsels tolerate it well.

The chloroquine phosphate protocol

Chloroquine phosphate (CP) is an alternative for fish that do not tolerate copper. CP is harder to source (requires a vet or specialty reef store, $40 to 80 per gram) but is more effective against ich, velvet, and brooklynella simultaneously.

Dosing: 40 mg of CP per gallon. For a 20 gallon QT, that is 800 mg.

CP does not test with any common hobby test kit. You must measure the powder precisely with a milligram scale.

Treatment duration: 30 days.

CP advantages: gentler on fish, treats more diseases. CP disadvantages: harder to source, harder to measure, more expensive.

Tank Transfer Method (TTM)

TTM is copper-free and works for ich only (not velvet, not brooklynella).

The protocol:

• Day 1: place fish in QT tank A
• Day 4: net the fish, drip-acclimate to QT tank B, leave tank A to dry and bleach
• Day 7: net the fish, drip-acclimate to QT tank A (cleaned and refilled), leave tank B
• Day 10: transfer to tank B
• Day 13: transfer back to tank A, fish has cleared the ich life cycle

The science: marine ich has a 6 to 8 day life cycle at 78 degrees. The trophonts on the fish must complete their cycle, drop off as tomonts, then release theronts (free-swimming infectious stage) to find a host. Transferring the fish every 72 hours means trophonts that have dropped off cannot find the host in the new tank, and the cycle is broken in 4 transfers.

TTM requires two tanks, two heaters, two filters. The doubled equipment cost is offset by no medication cost and faster total time (12 days vs 21 days for copper).

The observation period

Even after copper or TTM, a 14 day observation period in clean water is required before the fish enters the display. This catches:

• Brooklynella, which is not treated by copper
• Bacterial infections (vibrio, mycobacterium)
• Internal parasites that need praziquantel
• Lateral line erosion or other husbandry issues

During observation, run prazipro (praziquantel) for 5 days to clear flukes and tapeworms.

Exit criteria

A fish leaves quarantine when ALL of these are true:

• Copper treatment completed (or TTM completed) at least 21 days ago
• Praziquantel observation completed at least 7 days ago
• Fish has eaten consistently for 7 consecutive days
• No flashing, scratching, breathing irregularities, or spot disease for 14 days
• No new fish added to the QT during the final 14 days

Skipping any of these criteria risks importing disease into the display.

QT for sensitive species

Some fish do not tolerate copper or CP well. The alternatives:

• Mandarins, scooter blennies: TTM only, plus a 4 week observation in clean water with frequent feedings
• Angelfish (especially Centropyge dwarves): chloroquine phosphate is gentler than Cupramine
• Wrasses: half-dose Cupramine (0.25 ppm) for 28 days, plus prazi
• Sharks, rays: do not copper, run TTM only or rely on observation with very long QT periods

The display-tank fallow period

If your display has had a disease outbreak, the only cure is removing all fish to QT and leaving the display fishless for 76 days. During fallow:

• Maintain corals and invertebrates normally
• Run the tank at 80 degrees to speed parasite life cycle
• Continue normal water changes and feeding for corals
• No new fish, no rock additions, no equipment crossover from the QT

After 76 days, the parasites in the display have starved out. Fish returning from QT (assuming they completed full treatment) will not bring the disease back.

For marine setup, see our reef tank starter species guide and the marine tank cleaning crew guide. The /methodology page covers our QT trial protocol.

Frequently asked questions