Feeding Koi During Quarantine

By KoiQuanta Editorial Team|Updated Mar 2026

The feeding question comes up constantly with new fish. "Should I feed them? How much? What kind?" And the most important follow-up: "They're not eating - is that a problem?"

Yes. It's usually a problem.

Reduced appetite is one of the earliest, most reliable signs of stress or disease in koi. By the time you see visible symptoms - lesions, fin clamping, surface-gasping - you've already missed days of warning signs. Appetite tells you what's happening before anything else does.

Feeding during quarantine isn't just about nutrition. It's a daily health check you're running with every meal.

TL;DR

Their oxygen levels drop, CO2 rises, ammonia accumulates.
Feeding stressed fish causes two problems: 1.
Uneaten food rots in the quarantine tank, spikes ammonia, and stresses fish further 2.
Offer a small amount of food on hour 48 and watch what happens.
In a display pond, koi eat aggressively and you size meals to what they can consume in 5 minutes.
Start with half the normal ration on day 2–3 post-arrival and increase based on what you observe.
If food is sitting uneaten after 5 minutes, remove it immediately.

The First 48 Hours: Don't Feed

When new fish arrive - especially after an international shipment - don't offer food for the first 24 to 48 hours.

Here's why: shipping is profoundly stressful. Fish in transit bags have been in declining koi pond water quality tracker for hours. Their oxygen levels drop, CO2 rises, ammonia accumulates. When they arrive, they're in a physiological stress state even if they look healthy. Their digestive systems aren't running normally.

Feeding stressed fish causes two problems:

Uneaten food rots in the quarantine tank, spikes ammonia, and stresses fish further
Fish that eat but can't properly digest food develop additional internal stress

Instead, acclimate the fish to the quarantine tank temperature and chemistry. Run the air. Let them decompress. Offer a small amount of food on hour 48 and watch what happens.

Feeding Behavior as a Diagnostic Tool

Before I trained myself to track feeding daily in KoiQuanta, I'd sometimes not notice a fish had stopped eating for three or four days. By then, it was already showing other signs. Now feeding behavior is the first thing I check every morning.

Normal quarantine feeding behavior:

Fish approach food actively within 1–2 minutes of it hitting the water
Food is consumed within 5 minutes
No fish consistently hanging back or hiding during feeding

Early warning signs:

One or two fish not approaching food when others do
Fish approaching but spitting food out
Significantly reduced enthusiasm - taking 10+ minutes to finish a meal they'd normally finish in 2
Complete refusal

Any of these warrants closer inspection - behavior, respiration, visible symptoms, parameter test. Don't wait.

What to Feed in Quarantine

Wheat germ-based diet. Lower protein, highly digestible, and appropriate for fish that may be stressed or in cooler quarantine temperatures (65–68°F). Wheat germ-based foods reduce the waste load in the tank, which helps maintain water quality in a system without a strong biofilter.

Avoid:

High-protein growth feeds (more waste, higher ammonia production)
Color-enhancing foods (the astaxanthin and spirulina don't help a stressed or sick fish)
Medicated feed unless specifically prescribed - uncontrolled antibiotic delivery through feed promotes resistance

For fish actively undergoing antibiotic treatment: some vets prescribe medicated pellets. This only makes sense if the fish is eating reliably - a fish that's not eating won't receive a therapeutic dose through food.

How Much to Feed

Small amounts. Very small amounts compared to what you'd feed display pond fish.

In a display pond, koi eat aggressively and you size meals to what they can consume in 5 minutes. In quarantine, that rule still applies - but quarantine fish often eat less than display pond fish at the same temperature.

Start with half the normal ration on day 2–3 post-arrival and increase based on what you observe. If food is sitting uneaten after 5 minutes, remove it immediately. Every uneaten pellet is ammonia in the making.

During active antibiotic treatment, reduce feeding further - some protocols call for withholding food for 24 hours around each antibiotic dose to avoid drug-food interactions that reduce absorption.

Water Temperature and Feeding

Koi digestive systems are temperature-dependent. Below 50°F (10°C), don't feed - the fish can't digest food properly. Between 50–60°F (10–15°C), feed every 2–3 days with wheat germ. Between 60–68°F (15–20°C), once-daily small meals are appropriate. Above 68°F, twice daily is fine.

Most quarantine protocols target 65–68°F for KHV-risk fish, which puts you in once-daily territory. The digestive system is working, but not at peak efficiency. Don't push large meals.

Feeding and the Biofilter-Ammonia Problem

In quarantine tanks without established biological filtration - which is most quarantine tanks - uneaten food is the fastest path to an ammonia spike.

This is why feeding discipline in quarantine is stricter than in your display pond. In the pond, a few extra pellets get picked up by snails, filter-feeders, or decompose slowly in a large-volume system. In a 200-gallon quarantine tank, three uneaten pellets sitting overnight can measurably move your ammonia.

Feed small. Remove anything uneaten. Test ammonia daily.

Withholding Food During Treatment

There are specific situations where you should withhold food:

During formalin treatments: Formalin in the water column, fish not digesting normally, high metabolic stress. Skip feeding on treatment day.
During potassium permanganate dips: No feeding the day of treatment.
Fish showing no appetite: Don't force-feed. Offering food a sick fish won't eat just pollutes the water.
First 24 hours after transport: Already covered above.
Water temperature below 50°F: Digestion has essentially stopped.

For salt treatment and praziquantel, normal feeding continues unless fish are refusing food.