You have spent months building a beautiful, thriving community aquarium — carefully cycling the tank, selecting compatible species, growing in your plants, and establishing a stable ecosystem. All of it can be destroyed in under a week by a single fish carrying a common parasite that showed no visible symptoms at the store. Quarantine is not a suggestion for cautious hobbyists. It is the minimum standard of responsible fishkeeping, and this calculator tells you exactly what your specific situation requires.
Who Should Use This Calculator
This calculator is for any fishkeeper who is about to add new livestock to an established aquarium. That includes beginners adding their first fish to a newly cycled tank, intermediate hobbyists expanding an existing community, experienced aquarists adding wild-caught or imported specimens, breeders separating new broodstock from their breeding colonies, and anyone who has ever lost fish to a disease outbreak and wants to ensure it never happens again. If you are moving fish from one of your own tanks to another — even within the same household — a brief quarantine period is still strongly recommended, particularly if one tank has had any recent disease history.
Why Quarantine Is Non-Negotiable
The pet trade supply chain is long and stressful for fish. A single neon tetra sold at a big-box retailer may have changed hands four or five times: wild-caught or farm-bred in Southeast Asia, transported to a regional wholesaler, held in a crowded wholesale facility, shipped to a distribution center, transferred to the retail store, and then sold to you. At every stage, fish from different sources share water. Diseases — particularly Ich (Ichthyophthirius multifiliis), velvet (Oodinium), internal parasites, and various bacterial infections — spread readily in these conditions. The fish you see at the store may appear healthy because they are in the incubation phase of an infection that has not yet produced visible symptoms. That incubation period is exactly what quarantine is designed to catch.
The Perfect Quarantine Tank Setup
A quarantine tank does not need to be attractive or elaborate — in fact, simplicity is the point. The setup should prioritize ease of cleaning, medication effectiveness, and fish welfare, in that order. A tank between 10 and 40 liters is appropriate for most fish. Larger fish or multiple fish being quarantined together require more space, but the tank should not be so large that it requires huge volumes of medication.
The bottom should be completely bare — no substrate of any kind. Gravel and sand trap waste, harbor bacteria and parasites, and make it nearly impossible to vacuum effectively. More importantly, Ich completes part of its life cycle as a cyst on the substrate. A bare glass bottom means the cysts sit in open water and are exposed to treatment rather than protected in gravel. Cover the outside bottom of the tank with a dark-colored paper or mat to prevent fish from being stressed by their own reflection, which can look like a competitor or threat.
Hiding spots are essential for fish welfare but must be easily sterilized. Sections of PVC pipe in appropriate diameters, unglazed terracotta flower pots, and smooth river stones work excellently. Avoid anything porous or with crevices that cannot be thoroughly bleach-sterilized between uses. The goal is to give the fish a sense of security — a stressed fish has a suppressed immune system and will succumb to pathogens it might otherwise fight off — while maintaining a hygienic environment.
Filtration should be provided by a fully cycled sponge filter. A sponge filter is the ideal quarantine filter for three reasons: it provides both mechanical and biological filtration, it creates surface agitation for oxygenation, and it does not use replaceable cartridges that would need to be discarded and replaced every time medication is added. Critically, do not use carbon in the quarantine tank. Activated carbon removes medications from the water, making any treatment completely ineffective. If you have a hang-on-back filter with a carbon cartridge, remove the carbon and leave only the biological media during quarantine.
Maintain the quarantine tank at the temperature appropriate for the species being quarantined, and keep it stable with a reliable heater and thermometer. Temperature fluctuations stress fish and suppress their immune response at precisely the time you need their body to be fighting off any pathogens present.
Observation vs. Prophylactic Treatment — Understanding the Difference
There are two distinct philosophies for managing a quarantine period, and this calculator supports both. The observation-only approach involves placing fish in a bare quarantine tank and watching them closely for four weeks. Treatment is only applied if visible symptoms develop. This approach is appropriate for fish from genuinely trusted sources — a hobbyist breeder you know personally, a specialized breeder who certifies their stock, or fish moved between your own established tanks. The significant limitation of observation-only quarantine is that many of the most dangerous diseases have extended incubation periods or are subclinical carriers — the fish are infected but show no visible signs. Velvet in particular is notoriously difficult to detect until it is severe.
The prophylactic treatment approach — often called the Med Trio Protocol or the Aquarium Co-Op protocol — involves proactively dosing every new fish with a combination of medications during the first week of quarantine, regardless of whether any symptoms are visible. The logic is that the most common pathogens that threaten display tanks — Ich, flukes, internal parasites, and opportunistic bacterial infections — are so prevalent in the supply chain that assuming their presence is statistically safer than assuming their absence. Treating prophylactically costs a small amount of medication and time. Not treating and introducing a hidden parasite into a display tank costs potentially months of treatment and the lives of your existing fish.
The Med Trio Protocol — What It Treats and How
The Med Trio combines three medications that together cover the spectrum of the most common aquarium pathogens. Each targets a different category of disease and they are safe to use simultaneously at full recommended doses.
Ich-X (active ingredient: formaldehyde and malachite green) targets external parasites including Ich, velvet, and external fungal infections. It works by attacking the free-swimming and trophozoite stages of these parasites. Temperature elevation to 29°C to 30°C during treatment accelerates the Ich life cycle, causing more parasites to enter the vulnerable free-swimming stage simultaneously and improving treatment efficacy. Ich-X is dosed for 7 days, with a 50% water change before each new dose.
Praziquantel (available as Hikari PraziPro, Fritz Expel-P, or Aquarium Co-Op Paracleanse) targets internal and external parasites that Ich-X does not reach: flukes (Dactylogyrus and Gyrodactylus), tapeworms, and other flatworm parasites. These are extremely common in imported fish and almost invisible without a microscope. Praziquantel is typically dosed for 5 to 7 days.
An antibacterial medication — most commonly Erythromycin (Fritz Maracyn), Kanamycin (Seachem Kanaplex), or a broad-spectrum medication — targets gram-positive and gram-negative bacterial infections that may be present internally or externally. Columnaris, fin rot, and various ulcer-causing bacteria are common in stressed supply-chain fish and respond well to early treatment before they become systemic.
All three medications are added to the quarantine tank on Day 1 of the fish's arrival. This is not about treating sick fish — it is about clearing the most likely hidden pathogens before they can establish themselves or be transferred to a display tank.
The Day-by-Day Quarantine Timeline (Med Trio Protocol)
The timeline below describes a practical 30-day quarantine framework using the Med Trio approach as a first-week prophylactic treatment phase, followed by observation. Medication labels and species-specific requirements take priority over any general aquarium protocol. Do not combine this schedule with a separate disease-treatment protocol without following the instructions for the specific medication being used.
- Day 1 — Arrival and setup: Temperature-match the shipping water, then acclimate the fish gradually to the quarantine tank. Introduce the fish to a bare-bottom quarantine tank with hiding places and filtration, keep lighting subdued, and begin the selected prophylactic medications according to their product labels. Avoid feeding immediately after arrival if the fish is highly stressed.
- Days 2–6 — Treatment and observation: Observe the fish closely for changes in appetite, breathing, behavior, skin, fins, and feces. Keep feeding light and remove uneaten food promptly. Test ammonia regularly, especially in a newly established quarantine system. If a water change becomes necessary because of ammonia or other water-quality problems, follow the medication manufacturer's instructions for whether and how the removed medication should be replaced; do not automatically redose every medication by the same percentage.
- Day 7 — First-week assessment: Complete the first-week treatment phase according to the medication labels. Perform the water change specified by the products being used, reassess the fish, and remove medication residues when the treatment instructions call for it. If symptoms persist or a specific disease has appeared, switch to the appropriate targeted treatment protocol rather than assuming the prophylactic schedule is sufficient.
- Days 8–14 — Early observation: Continue stable water quality, normal species-appropriate feeding, and daily observation. Do not treat a symptom-free fish with additional medication simply to fill a calendar; extend or restart quarantine when disease is detected or treatment is required.
- Days 15–30 — Standard observation window: Continue quarantine and watch for delayed or previously subclinical disease signs. A 30-day observation period is a practical minimum framework for many store-bought, shipped, or otherwise uncertain-source fish, but it is not a guarantee that every pathogen has been excluded.
- Day 31+ — Transfer decision: Move the fish only after the appropriate quarantine period has been completed, the fish is eating normally and clinically stable, and any required post-treatment symptom-free observation period has elapsed. Match temperature and water chemistry gradually during transfer, and avoid transferring quarantine water into the display tank.
Protocol note: A prophylactic Med Trio schedule should not be confused with the daily water-change and re-dosing instructions used for an active Ich-X disease treatment. If Ich, velvet, bacterial disease, or another condition is diagnosed, follow the treatment product's current label and the targeted disease protocol instead of treating this timeline as a substitute.
Reading New Fish for Early Warning Signs
Even during a prophylactic protocol, careful daily observation is essential. Some conditions require specific treatments beyond the Med Trio, and catching them early dramatically improves outcomes. Look for white spots resembling salt or sugar grains — classic Ich. Look for a fine gold or rust-colored dust on the body, most visible under a flashlight at a low angle — this is velvet (Oodinium), which is far more lethal than Ich and progresses faster. Check for frayed, ragged fin edges — fin rot. Look for rapid gill movement or gasping without a water quality explanation — possible fluke infestation or bacterial gill disease. Watch for hollow bellies and stringy white feces — internal parasites or wasting disease. Any of these findings should prompt you to address the specific condition in addition to the standard Med Trio protocol, and the quarantine clock should be extended accordingly.
When It Is Safe to Move Fish to the Display Tank
The quarantine period ends only when all of the following conditions are met: the minimum quarantine duration (14 or 30 days, depending on source) has elapsed, the fish have been symptom-free for at least 14 consecutive days after the final day of any treatment, water parameters in the quarantine tank are stable and the fish are eating well, and no new fish have been introduced to the quarantine tank during the observation window (which would restart the clock for all fish present). Acclimate the fish from the quarantine tank to the display tank gradually — a 30-minute float to temperature-match, followed by a slow drip or cup-acclimatization to chemistry-match, prevents shock even between tanks with similar parameters.