Sinking vs floating food for goldfish

Pick up two tubs of goldfish pellets and the difference between them may be a single word on the label: floating or sinking. It sounds like a detail. For a comet in a pond it more or less is. For an oranda, a ranchu or a pearlscale it changes the posture the fish feeds in, how much air it swallows, and, many keepers believe, how likely it is to develop the buoyancy problems those breeds are known for.

Sinking versus floating food

Floating food The fish tips nose-up to take food from the surface and swallows air with it. Aerophagia, the swallowing of air, is a recognised cause of buoyancy trouble in fancy goldfish.

Sinking food The fish stays level. Sinking or pre-soaked food means less air is swallowed. Soak dry food for a minute if it does not sink on its own.

Why fancy goldfish do better on sinking food

Watch a fancy goldfish eat floating pellets. It angles its body upward, breaks the surface with its mouth, and snaps at each pellet with a gulp that takes in air as well as food. Some of that air is spat out, some passes through the gut, and some, many keepers believe, ends up affecting the fish’s buoyancy in ways its compressed body cannot easily correct.

The evidence for the air-gulping link is observational: keepers noticing that round-bodied fish on floating food tip and bob more, and that switching to sinking food often settles them. There is no controlled evidence, and buoyancy trouble has several causes, infection among them. But the change costs nothing, the fish feeds head-down, and the practical experience behind it is broad enough that this site recommends sinking or slow-sinking food for fancy breeds. The oranda, the ranchu and the pearlscale, three round-bodied fancies, are breeds where keepers report it.

A fish that is already tipping or floating needs more than a change of food. Floating upside down walks through the possible causes, from constipation to water quality to infection, and how to work through them.

When floating food is fine

Single-tailed goldfish, the commons, comets and shubunkins, are comfortable surface feeders. Their long bodies seem to handle the upward tilt without strain, and keepers report no particular tendency to buoyancy trouble on floating food. For them the choice between floating and sinking is a matter of convenience.

In a pond, floating food is usually the better choice. It brings the fish up where you can see them, which is your daily health check, and it lets you judge exactly how much has been eaten. Sinking food in a pond vanishes into the bottom where it may or may not be found. Goldfish ponds covers pond feeding through the seasons, including when many keepers stop altogether.

Floating food also has one real advantage in any tank: leftovers are easy to see and easy to scoop, which makes it harder to overfeed without noticing.

Does it actually sink? Test it

Worth a minute before trusting the word on the tub, because the label is not always a reliable description.

Drop a dozen pellets into a glass of tank water and watch.

• True sinking: down within a few seconds, and sitting on the bottom of the glass.
• Slow-sinking: drifting down over roughly ten to twenty seconds, which is the behaviour most useful in a mixed tank.
• Floating: still on the surface after a minute.

Three reasons the test earns its minute. Labels vary in meaning between manufacturers, and some “sinking” pellets are really slow-sinkers. Formulations change between batches without the packaging changing. And a tub that has been open in a humid kitchen behaves differently from a fresh one, because pellets that have absorbed moisture sink faster and break up sooner.

While the glass is there, note how long a pellet holds together before it starts to cloud the water. A food that disintegrates within a minute is one that will foul a tank if any of it is missed, which matters more for a sinking food than a floating one because you are less likely to see the leftovers.

Making floating food sink

If you have a tub of floating pellets and a fancy goldfish, you do not need to throw it away. Put the portion in a small cup, add a little tank water, and leave it for a minute or two. Most floating pellets take on water and sink as soon as they are wet through; a stir speeds it up. Pour the lot in, or lift the pellets out with a spoon and release them near the bottom. Flakes sink the same way in a few seconds. Soaking leaches some of the water-soluble vitamin content, which is why an aquatic vet advises against it; keepers of fancies accept the trade, and it is only necessary while the tub lasts, since the next one can be a sinking formula. Gel food sinks by nature and is the other easy answer.

Soaking, and how to get it wrong

The method is simple and there are three ways to spoil it.

Too long. A pellet left in water for ten minutes is not a sinking pellet, it is mush, and it clouds the tank and fouls the substrate. One to two minutes is enough for most foods, and the glass test above tells you how long yours actually needs.

Too much water. Use a small cup with just enough water to wet the portion. Tipping a mugful of soaking water into the tank adds nothing useful and dilutes the point of measuring a portion in the first place.

Tap water. Use water from the tank. It is right there, it is the right temperature, and it avoids adding a small dose of untreated tap water at every meal.

And remember it is a temporary measure: the next tub can be a sinking formula. Reading a fish food label covers choosing one.

The middle ground: slow-sinking pellets

Between the two extremes are pellets designed to drift down through the water over ten to twenty seconds, feeding fish at every level before settling. Many keepers of mixed tanks, or of fancies that are slow to find food on the bottom, settle on these. They avoid the surface gulp, they do not disappear into the substrate as fast as a true sinking pellet, and they spread the food through the tank so a group has room to feed. The pellet guide covers what else to look for on the label.

Feed it somewhere you can see it

The practical answer to the one real weakness of sinking food, and it is rarely suggested.

Use a dish. A shallow ceramic or glass saucer, set on the substrate in an open spot, with the portion dropped into it. What that buys you:

• Nothing vanishes between stones. A pellet in a dish is a pellet you can account for.
• The two-minute test works again. You can see exactly what is left, which is the usual way of judging a portion — the feeding guide covers why that test is easily defeated by gravel.
• Leftovers lift out with the dish rather than being hunted with a siphon.
• The fish learn where it is within a few days, which concentrates a scattered group at feeding time and makes it obvious if one is not coming.

Or remove the problem instead. A substrate that cannot swallow a pellet — sand, a bare bottom, or stones too large to hide one — achieves the same thing without the dish, and the substrate guide covers why goldfish tanks tend toward those anyway.

A feeding ring does the equivalent job for floating food, holding it in one place instead of letting it drift to the filter outlet and sit in the back corner for a week.

Where every other food sits

The question this page is really about applies to the whole diet, and the answer is not the same for each.

• Flakes: surface, then everywhere. They float briefly, then waterlog and drift, which means a fancy still gulps at the surface for the first ones and the rest end up scattered. Goldfish flakes covers their other drawbacks, chiefly how readily they take up air and moisture once opened.
• Gel food: sinks. It is made with water and goes straight down, which is one of the reasons it suits fancies — gel food covers the rest.
• Frozen bloodworm and daphnia: sink, slowly. Thawed and released near the bottom they suit a fancy well; dropped in frozen they scatter as they thaw. Frozen food covers thawing properly.
• Vegetables: depends how you prepare them. A blanched pea sinks. A leaf of spinach or lettuce floats until it is waterlogged, which is why many keepers clip greens to the glass at mid-depth or weight them with a stone — vegetables for goldfish covers what to offer.
• Live food: wherever it goes. Bloodworm burrow, daphnia swim in the water column, and the chase is part of the value — live food covers the trade-offs.

So a diet built on sinking pellets with vegetables and a frozen treat is naturally a low-surface diet, which is the goal for a fancy, and it does not require any special effort beyond preparing each item the way it wants to be prepared.

Feeding a fish that cannot reach the food

A sharp version of this page’s question, and the one situation where getting it wrong means the fish does not eat at all.

A fish that floats cannot get down to sinking food. It hangs at the surface while the portion settles onto the substrate out of reach, and it can go hungry in a tank where food was provided. For that fish, floating or slow-sinking food delivered where it actually is, is the correct answer — the opposite of the advice everywhere else on this page.

A fish that sinks cannot get up to floating food, for the same reason in reverse. Sinking food placed near it, or a dish set where it rests, solves it.

A fish with poor eyesight — a telescope, moor or celestial, or an oranda whose wen is beginning to cover its eyes — has to find food with smell, taste and the lateral line as well as what it can see, which can take longer; treat a celestial’s vision as unreliable. It needs food that stays put rather than drifting, and time.

A fish recovering from illness or under treatment often eats reluctantly and slowly, and will be beaten to anything by its tank mates. Feeding a sick goldfish covers what and how to offer; the placement principle is the same as above.

The general rule worth extracting: feed to where the fish is, not to where the book says the food should go. The advice for fancies exists to prevent a problem, and once a fish has the problem the advice is subordinate to the fish eating.

Changing a fish to a new food

Goldfish are conservative about food, which surprises people who have watched one eat gravel.

A fish moved abruptly from floating flakes to a sinking pellet will often ignore the new food for days — it does not recognise it, it is not where food normally appears, and it may not smell like anything the fish associates with eating. Owners conclude the fish is ill or the food is bad, and go back.

The method that works:

• Mix, do not switch. Start with mostly the old food and a little of the new, and shift the proportion over a week or two.
• Feed the new food to a hungry fish, at the start of a meal rather than after it has filled up on the familiar one.
• Put it where the fish will find it. A new sinking pellet dropped into a dish where the old food used to arrive gets investigated faster than one scattered into gravel.
• Give it several days. A few refusals mean very little. A week of refusing everything, including the old food, is a different question and belongs with loss of appetite.

And do not starve a fish into accepting something. A day or two of light feeding while a new food is introduced is reasonable; a fasting standoff is not, and it is particularly unwise with a juvenile or a fish that is already thin.

In a pond

Floating is the default outdoors, for a reason that has nothing to do with the fish’s anatomy.

You can see it. Pond fish are viewed from above through water that is rarely clear, and floating food brings them to the surface where a daily count and a look at each fish is possible. That observation is a useful daily health check — goldfish ponds covers the rest.

And you can judge the portion. Uneaten floating pellets are visible and scoopable; uneaten sinking pellets vanish into the bottom to rot, which in a pond is a slow contribution to exactly the problem the filter is fighting.

The exceptions. Fancy goldfish summering outdoors have the same anatomy they have indoors, so sinking or soaked food suits them there too. And in cool water, the wheatgerm-based foods used at the ends of the season, which makers call easily digested, are often sinking or slow-sinking formulations — feeding through the seasons covers the temperature bands and when many keepers stop altogether.

Making sure everyone gets fed

Sinking food has one weakness: it is harder to see who is eating it. Pellets that land behind a rock or in a corner may be found by the boldest fish and missed by the rest, and in a tank with an oranda whose wen is beginning to cover its eyes, or a telescope or bubble eye with poor vision, a shy fish can go short for weeks without anyone noticing.

Scatter the portion across an open area rather than dropping it in one spot. Feed at more than one place if the tank has a bully. Keep the bottom simple, with sand or large smooth stones rather than gravel that swallows pellets, so food stays where the fish can reach it. And once or twice a week, watch a whole feed from start to finish and check that each fish has a full, gently rounded belly afterward. In a mixed tank of fancies and single-tails, the fast fish will take the surface and the mid-water; drop a few sinking pellets in a corner for the slower ones a moment later, and consider whether the mix is fair to the fancies at all.