How often to feed fish, and how much

How often

For adult aquarium fish the welfare guides agree on once a day. RSPCA Australia says to feed tropical fish once a day; OATA's goldfish care sheet says the same for goldfish. The RSPCA's UK guide adds that it is better to underfeed than to overfeed.

Fish that are still growing are different. Chewy's vet-reviewed guide notes that small fish have faster metabolisms than large ones and generally need more frequent feeding, and advises against fasting juvenile fish for more than 12–24 hours. For fry and young fish that means several small meals across the day, each still small enough to be finished.

How much: the two-minute rule

The amount is set by time, not by a scoop. RSPCA Australia: only what can be eaten in under two minutes. The RSPCA in the UK: as much as the fish eat within 2 to 5 minutes, starting small and adding a little more only if they still seem hungry. OATA: what goldfish can eat within a few minutes.

• Watch the whole meal. Food that reaches the substrate and stays there was too much.
• Feed where everyone can reach. RSPCA Australia suggests feeding in two or more separate areas when there are several fish, so the fastest eaters don't take everything.
• Remove what's left. Uneaten food breaks down and contaminates the tank (RSPCA Australia); a quick siphon or net after the meal stops it rotting.

Why overfeeding is the usual mistake

RSPCA Australia calls overfeeding the most common problem with all fish, leading to obesity and other health problems. The bigger risk is to the water. OATA explains that excess food builds up and breaks down, releasing toxic waste, and UF/IFAS calls overfeeding a major cause of high ammonia: the more fish are fed, the more ammonia they excrete, and uneaten food adds more. In a new tank, whose filter bacteria are still growing, that extra ammonia has nowhere to go. Our high ammonia page covers what to do when a test shows it, starting with cutting back the food.

Fish that need a different routine

• Young fish and fry. More often, in smaller amounts (Chewy).
• Night feeders. The RSPCA says nocturnal species, such as some catfish, should be fed in the evening, when they are active.
• Sick, stressed or thin fish. Chewy's guide says these need regular feeding rather than fasting.
• Grazers that hunt all day. Bulk Reef Supply calls feeding the most important part of mandarin dragonet care: wild-caught mandarins often refuse anything other than live copepods and can starve in a tank that looks healthy. Our mandarin dragonet care sheet covers captive-bred fish that take prepared food.

Holidays and missed meals

Chewy's vet-reviewed guide says most healthy adult fish can go three to five days without food without lasting consequences, so a long weekend away needs no special arrangement for a tank of healthy adults. Juveniles, and sick or thin fish, are the exception.

For anything longer, skip the holiday feeding blocks. The RSPCA advises against them because they dump a lot of food into the water at once, and Chewy notes they don't always dissolve evenly. The RSPCA's alternative is to pre-pack each meal, so whoever looks after the tank feeds a measured portion rather than guessing, which is how well-meaning sitters overfeed.

Signs you're feeding too much

• Food left on the substrate or in the plants after the meal.
• Ammonia or nitrite showing on a test in an established tank (see high ammonia).
• Nitrate climbing faster than your water changes remove it (see high nitrates).
• A milky haze in an established tank: a bacterial bloom feeding on a sudden nutrient pulse (see cloudy aquarium water).

The fix for all four starts in the same place: smaller meals, eaten in full. The water change calculator helps size the change while the tank settles.