What to Feed Koi and Pond Fish: A Canadian Owner's Guide

Feed koi and pond fish a high-quality staple pellet sized to their mouths, and let water temperature — not the calendar — decide how much and how often. Above 15°C, koi digest protein-rich food readily and can be fed once or twice daily. Between 10 and 15°C, cut back to every second or third day. Below 10°C, stop feeding entirely until spring. In Canada that last rule matters more than anywhere else: feeding too late into a cold fall is one of the most common causes of overwinter koi losses.

Why water temperature decides everything

Koi and goldfish are cold-blooded. They do not regulate their own body temperature, so their entire metabolism runs at the speed the water allows. In warm summer water they process protein quickly and grow fast. As Canadian water cools through fall, digestion slows dramatically — and food sitting half-processed in a cold fish's gut can decompose internally before it is digested, which causes serious and often fatal problems.

This is why the most useful piece of koi-keeping equipment in Canada is not a premium food. It is a pond thermometer. Air temperature tells you very little; a pond can sit at 12°C for a week after the first frost, and it can drop 5 degrees overnight when a cold front arrives. Feed to the water, not to the forecast.

The Canadian feeding calendar

Spring start-up

Koi come out of winter with depleted reserves but a still-sluggish metabolism, and this is when impatience does the most damage. Wait until water holds above 10°C — typically mid-to-late April in southern Ontario — then start with a small feed every second or third day. Watch how quickly it is taken. Appetite strengthens gradually through the teens; by the time water reaches 15°C you can move to daily feeding.

The growing season

Between 15 and 25°C, koi put on size and colour. Feed a quality staple pellet once or twice daily. Aquascape Premium Staple Fish Food Pellets are formulated for exactly this everyday role, with balanced protein for all common pond fish.

Heat waves

Above about 27°C, ease off. Warm water holds less dissolved oxygen, and digestion is oxygen-hungry work — a heavy feed on a 30°C afternoon is how healthy fish end up gasping at the surface by evening. Feed early in the morning and make sure your aeration system is running. A fountain or aerator does its most important work of the year on the hottest days.

Fall wind-down

This is the part Canadian owners most often get wrong. As water falls through 15°C toward 10°C, taper frequency deliberately — every second day, then every third. Southern Ontario ponds usually cross the 10°C line somewhere in mid-to-late October, earlier north of Barrie and in cottage country. Once you stop, stay stopped. Koi will sometimes rise and mouth at the surface on a mild November afternoon. They are not hungry; they are responding to light and movement. Do not feed them.

Winter

Below 10°C, koi enter a dormant state called torpor, resting near the pond bottom and living off body reserves. They eat nothing for months and this is entirely normal. What they do need is gas exchange — under a sealed ice cap, decomposition consumes oxygen and traps carbon dioxide and methane, which is what causes winterkill. Keeping an opening in the ice with a de-icer or a shallow diffuser is the winter equivalent of feeding. See our guide to installing a pond de-icer in Ontario.

How much: the five-minute rule

Offer only what your fish finish completely in about five minutes, then net out anything left over. This single habit solves most feeding problems.

Uneaten food is the number-one avoidable source of pond water trouble. It breaks down into ammonia and phosphates, clouds the water, feeds algae, and adds to the muck layer on the bottom. If pellets are still floating after five minutes, you fed too much — skim them out and reduce the next portion.

Two smaller feedings beat one large one during peak season. And be sceptical of your fish's enthusiasm: koi that surge to the surface when you approach are not necessarily hungry, they are trained. A healthy adult koi can comfortably go a week or two without supplemental food in summer, and the entire winter without any. Vacations are not a feeding emergency.

Which food for which fish

Pellets are the right staple for koi and larger goldfish. They hold together in water, float where you can see exactly what is being eaten, and deliver complete nutrition.

Flakes suit smaller goldfish and young fish with small mouths. Aquascape Premium Fish Food Flakes do the same nutritional job in an easier bite. In a mixed pond, match food size to the smallest mouths so everyone can feed.

Treats have a place. Koi Krunchies are the hand-feeding food that turns koi into pets that eat from your palm — fed a few pieces at a time, not by the handful, and kept to a small share of the overall diet.

The full range is in our Fish Food & Care collection.

What not to feed koi

Bread is the big one. It offers koi essentially no nutrition, swells in the digestive tract, and whatever is not eaten breaks down quickly and fouls the water. The same applies to crackers, cereal and other processed human food.

Also avoid: anything oily or salted, dog and cat food, and cheap fish food with unspecified filler as the first ingredient — high filler content means more waste passing straight through into your water.

Safe kitchen treats

In small amounts during warm water, koi will happily take shelled peas, lettuce, spinach, and small pieces of watermelon or orange. Treat these as occasional variety, not nutrition — a few pieces alongside a normal feed, never as a meal replacement, and always removed if uneaten.

Feeding and water quality are the same job

Every gram of food you add ends up in the water one way or another. If you are feeding generously, you have to manage the downstream effects:

• Test for ammonia if fish look stressed after a heavy feed. An ammonia neutralizer handles spikes quickly.
• Keep filtration adequate for your stocking level. Pond filtration that was sized for six fish will not cope with sixteen.
• Keep the water moving. Well-fed fish in still, warm water is the classic setup for a summer fish kill. Serious koi keepers treat aeration as fish-care equipment, not decoration.
• Address green water at the source. Feeding drives nutrient load, which drives algae. A UV clarifier clears suspended algae without chemicals; for filamentous growth, see our algae control range.

Stressed fish eat poorly

Appetite is one of the best health indicators you have, which means a fish that stops eating is telling you something. Before assuming a food problem, check for predators. Herons and raccoons are relentless in Ontario ponds, and fish under sustained predation stop feeding and stay deep.

Cover solves it. A shelter like the Aquascape faux log fish cave gives koi and goldfish somewhere to retreat from predators and a shaded refuge in summer heat. Predators kill more appetites than bad food does.

Frequently asked questions

What should I feed my koi every day?

A quality staple pellet sized to your fish, fed by the five-minute rule once or twice daily in water above 15°C. Flakes suit smaller fish. Treats such as Koi Krunchies are supplements, not the base diet.

Can koi eat bread?

No. Bread has essentially no nutritional value for koi, can swell in the digestive tract, and leftovers break down and pollute the pond. Offer shelled peas, lettuce or small fruit pieces instead.

When should I stop feeding koi in Canada?

When water temperature drops below 10°C and stays there — typically mid-to-late October in southern Ontario, earlier further north. Use a pond thermometer rather than judging by air temperature.

Why can't I feed pond fish in winter?

Below about 10°C their digestive system effectively shuts down, and food eaten in cold water can decompose internally before it digests. Your fish are not starving — they are dormant, which is normal for Canadian ponds.

How long can koi go without food?

All winter in cold water, which is exactly what they do under the ice. In warm summer water, healthy fish in an established pond with natural forage manage a week or two without supplemental feeding.

Can koi and goldfish eat the same food?

Yes. Quality staple pellets and flakes are formulated for all common pond fish. Match the food size to the smallest mouths in the pond so every fish can feed.

Do koi eat algae?

Koi graze on soft algae and plant matter as a natural part of their diet, but grazing will not control an algae problem. That takes nutrient management and aeration.

My fish aren't eating in spring — should I worry?

Check water temperature first. Appetite returns gradually as water passes 10°C and strengthens through the teens. If water is warm and fish still refuse food, look for stress factors: predators, low oxygen, or a water-quality issue.

How much should I feed koi at once?

Only what they finish completely in about five minutes. Net out anything left after that and reduce the next portion. Uneaten food is the leading avoidable cause of ammonia spikes and algae blooms.

Questions about feeding, fish health, water quality or overwintering koi? Email info@fountaindepot.com or call 905-752-1226 — advice backed by 50+ years of pond and fountain service in the Greater Toronto Area. Fish food and pond care products ship across Canada from Markham, Ontario.