Saltwater Fish Quarantine & Treatment Guide — Ich Prevention Basics

Quarantine (QT) and treatment are the most critical processes when introducing new marine fish to a tank. Neglecting this process risks pathogenic agents introduced by a single fish spreading throughout the entire tank, potentially resulting in the loss of all fish. In particular, marine fish ich (white spot disease, caused by Cryptocaryon irritans) is an especially troublesome disease that becomes extremely difficult to completely eradicate once it enters the main tank.

Why Quarantine is Necessary

Most diseases in marine fish are introduced when new fish are added to the tank. Even if fish appear healthy, they often carry pathogens in a state of reduced immunity due to stress. It is not uncommon for latent diseases to manifest as a result of transport stress or environmental changes.

Cryptocaryon, the causative agent of marine ich, lurks as cysts (dormant forms) in the live rock and substrate of the main tank, and will recur repeatedly once conditions are favorable. In reef tanks with corals and anemones, copper ion therapy cannot be used, making treatment options extremely limited once the disease is introduced. Pre-treating in a quarantine tank is the only reliable preventive strategy. Quarantine tank setup

A quarantine tank should be established as a completely independent system separate from the main tank.

Required equipment: A 45–60 cm tank, an external hang-on filter or sponge filter, heater, air pump, and hiding places such as PVC pipes (live rock cannot be used due to copper treatment). Do not add substrate. Sand substrate absorbs medication and allows parasitic cysts to lurk.

Water quality management: Use the same synthetic seawater as the main tank, maintaining a specific gravity of 1.023–1.025 and a water temperature of 25–26°C. Since quarantine tanks hold less water, water quality deteriorates easily, requiring daily water testing and frequent water changes. Maintain levels where ammonia and nitrite are undetectable.

Establishing a biofilter: The quarantine tank filter also needs bacteria. A simple approach is to transfer some filter media from the main tank's filter. However, since copper treatment damages bacteria, frequent water changes are needed to manage ammonia during treatment.

Basic Quarantine Procedure

Quarantine a newly acquired marine fish using the following steps.