Homemade goldfish food

The gel food page mentions that many keepers blend their own and then stops. This is how, and it starts with the catch.

Homemade food is easy to get approximately right and hard to get properly right. Protein, fat and fibre are easier to approximate by eye. Vitamins and trace minerals are not, and a formulated food carries a premix that has been designed and tested for the purpose. No kitchen recipe replicates it.

That is not an argument against making your own. It is an argument for one specific ingredient, below.

What it is good at

Freshness and variety. A gel cube of blanched vegetables and real seafood is a different thing from a pellet that has been in a tub since March.

Control. You know exactly what is in it, which is more than the label on most tubs will tell you.

Vegetable content. Goldfish are omnivores that eat a good deal of plant matter, and getting real plant matter into them is easier in a gel than in any dry food.

Tempting a reluctant fish. Strong-smelling fresh food is often taken by a fish that has ignored pellets for days, which is genuinely useful when feeding a sick goldfish.

Texture. Soft, sinking and slow to break up, which keepers find suits deep-bodied fancies; the gel page sets out the reasoning.

The version most people should actually make

Blanched vegetables, in the tank, with no binder and no blender.

A slice of courgette, a leaf of spinach, a few deskinned peas — blanched for a minute, cooled, and either clipped to the glass or dropped in. Two minutes of work, no freezer, no hygiene questions, and it delivers most of what homemade food is for: fresh plant matter and variety in a diet that is otherwise dry pellets. The vegetables page covers which ones suit goldfish and how to prepare each.

If you only ever do this and never make a gel, the fish are not missing much.

The middle option

Worth naming, because the choice is not only between a pellet and a kitchen.

Commercial gel mixes are sold as a powder you combine with hot water and set yourself. They carry the formulated vitamin and mineral package, they set reliably, they take five minutes rather than thirty, and they cost more per gram than either a pellet or a home mix.

They are the sensible answer for anyone who wants the gel format — soft, sinking, well suited to fancy goldfish — without the balance question or the raw seafood. And they take homemade additions perfectly well: a commercial gel base with your own blanched vegetables blended in is arguably the best version of everything on this page, since the vitamin and mineral package comes already formulated rather than approximated.

The gel food page covers the format itself and where it fits against pellets and frozen food.

The ingredient that helps with the balance problem

The binder: agar, not gelatin

Both set a mix into a sliceable block. They behave very differently in a tank.

Gelatin sets in the fridge and softens again at around body temperature. In a goldfish tank at 22 °C it holds, more or less; in a warm summer tank it begins to dissolve, which clouds the water and fouls it faster than the fish can eat.

Agar must be boiled to dissolve, sets firmer, and stays solid at any temperature a goldfish tank reaches. It is also vegetarian.

For goldfish, agar is the better choice and the difference is worth the extra step of boiling. Gelatin is acceptable in a cool tank if it is what you have.

What you need

Almost nothing, and probably all of it already:

• A blender or a stick blender
• A saucepan for the agar
• A shallow tray, or an ice cube tray for portioning
• A sharp knife
• Freezer bags or a lidded box
• A small spoon kept for feeding

No equipment on that list is worth buying specially, which is part of the appeal.

How big a batch

Worth working out before you start, because a common outcome of an enthusiastic first attempt is a freezer drawer of gel that is still there a year later and no longer worth feeding.

A goldfish eats a very small amount of gel per meal — a cube roughly the size of the fish’s eye, two or three times a week if the rest of the diet is pellets. For two or three adult fancies that is somewhere around a small handful of cubes a week.

Which means a batch made in a single ice cube tray will typically last two or three fish well over a month, and a tray-sized slab cut into small cubes lasts considerably longer than the three months it should be used within. Make less than feels worthwhile, use it up, and make it again — the batch takes half an hour whatever its size, and fresh is the whole point.

Ingredients, sorted

Use freely	Use sparingly	Keep out
Peas, deskinned and blanched	Spinach, blanched — in moderation	Bread, crackers, biscuit
Kale, courgette, broccoli, blanched	Sweet potato — starchy	Anything salted or seasoned
White fish, cooked through	Mussel, cooked through — rich	Mammalian meat and fat, including beef heart
Prawn or shrimp, cooked, shell on	Bloodworm — rich	Oils, butter, sauces
Earthworm, chopped	Egg — occasionally	Citrus, onion, avocado
	Garlic — a drop, as flavour	Anything from a ready meal
	Spirulina — a supplement, not a base

Three notes worth having.

Prawn shells are worth keeping in. They carry astaxanthin, which deepens colour, and chitin, which contributes fibre. Blend them thoroughly.

Cook the seafood through before blending. Some raw fish and shellfish contain thiaminase, a heat-labile enzyme that breaks down thiamine — vitamin B1, which is part of the B group the ground pellet is in the mix to supply. Carp, goldfish and minnows are among those documented, which is why the table above says cooked through rather than raw. The risk is not a one-off: thiaminase does nothing to a fish that eats an occasional piece, and matters only when such an ingredient is a staple, which is what a batch of homemade food can make it.

The fix costs nothing. Heat inactivates the enzyme, so cook the fish and shellfish through, then drain and blend. If you would rather not cook anything, keep raw seafood occasional and let earthworm, bloodworm and the ground pellet carry the protein instead.

Beef heart and other mammalian meat are best left out. Nothing shows a goldfish needs them, and keepers avoid mammalian fat as a precaution.

A working recipe

Proportions by rough volume rather than precise weights, because the ingredients vary and this is not chemistry; they are ingredient shares, not nutrient levels.

Component	Share	Examples
Vegetable matter	~45–50%	Deskinned peas, spinach, kale, courgette, broccoli — all blanched
Protein	~30%	White fish, prawn or shrimp, mussel (all cooked through), bloodworm, earthworm
Ground pellet	Part of the remainder	A good-quality goldfish pellet, powdered; how much is enough is not established
Agar	To set	Follow the packet; usually a small spoonful per batch
Optional	A trace	Spirulina powder, a drop of garlic extract

Method:

1. Blanch the vegetables and cook the seafood. Vegetables need a couple of minutes in boiling water, then drain; fish and shellfish need cooking through. Blanching softens the vegetables, so they blend smoothly.
2. Blend everything except the agar with a little tank or dechlorinated water, to a thick paste. Not a liquid.
3. Dissolve the agar in boiling water separately, following the packet.
4. Combine quickly while the agar is still hot, and mix thoroughly.
5. Pour into a shallow tray, a centimetre thick or less. Thin sets faster and portions better.
6. Chill until firm, then cut into cubes sized for your fish.
7. Freeze in a single layer on a tray, then bag the cubes so they do not fuse into a block.

A batch takes about half an hour and lasts a few goldfish for months.

Hygiene, which is the part people skip

You are preparing raw fish and shellfish in a kitchen. The rules are the ones you already know.

• Clean surfaces, boards and the blender afterwards as you would after preparing seafood for yourself.
• Freeze promptly, in thin sheets so it freezes fast.
• Use within about three months.
• Never refreeze a thawed portion.
• Do not leave thawed food out. Thaw a cube in a little tank water immediately before feeding.
• Keep it labelled and separate in the freezer, which matters more in a shared household than it sounds.

When the batch goes wrong

Problem	Cause	Fix
It never set	Agar not properly boiled, or too much water in the paste	Reboil with the agar dissolved separately; blend the paste thicker
It sets and then dissolves in the tank	Gelatin in a warm tank	Use agar
It clouds the water	Too soft, over-wet, or left in too long	More binder, thicker paste, remove faster
It crumbles when cut	Too little binder, or cut while still warm	More agar; chill fully first
It is rubbery and ignored	Too much agar	Less binder; cut smaller
Faeces go long and pale after switching	The mix is too rich	More vegetable, less protein; see constipation
The fish take it and the tank fouls	Overfeeding — it replaced nothing	It substitutes for part of the ration, not adds to it

Feeding it

Thaw first. Dropping a frozen cube into the tank puts a cold lump in front of a fish and thaws slowly enough to foul the water. A minute in a spoonful of tank water is enough.

It replaces part of the ration, it does not add to it. A gel cube plus the usual pellets is simply overfeeding.

Remove what is not eaten, quickly. Gel food is soft and breaks down faster than a pellet, so anything left after a couple of minutes should come out.

Two or three times a week is a reasonable place for it, with a formulated food doing the rest — which is the balance the nutrition page and the how often to feed guide both describe.

Getting them to eat it

Expect rejection at first. Fish are wary of unfamiliar food, and a keeper who concludes on day one that the batch is a failure has usually just met ordinary neophobia.

• Introduce it alongside the usual food, not instead of it. A small piece of gel dropped in with the pellets they already take.
• Give it several days. Most goldfish come round within a week; some take longer.
• Cut it smaller than you think. A cube a fish cannot get its mouth around is a cube it ignores.
• Try it when they are hungry, at the first feed of the day rather than the last.
• Do not leave it in while you wait. Remove uneaten gel after a couple of minutes and try again tomorrow.

If they genuinely will not take it after a fortnight, the likely causes are that it is too firm — too much agar — or too large, rather than anything about the ingredients.

Variants worth making

The base recipe is a starting point. Four adjustments cover most situations.

For growing fish. Raise the share of protein-rich ingredients and drop the vegetable share accordingly, using white fish and prawn rather than the richer shellfish. These are ingredient proportions, not nutrient levels, so there is no protein percentage to aim for from the kitchen; the growth page covers growth in the first years.

For cool water, autumn and spring. Reverse it: a smaller share of protein-rich ingredients, a larger vegetable and cereal share, and wheatgerm if you have it. This follows the tradition the seasonal feeding page describes, with the same caveat: wheatgerm is the traditional cool-water choice rather than a tested one.

For a fancy prone to buoyancy trouble. More vegetable, more fibre, less of everything rich, and cut the cubes small. Keepers report that a soft sinking gel helps some fancies that tip; there is no controlled evidence, and infection is among the causes, which the buoyancy page covers.

For colour. Shell-on prawn, krill, spirulina, and orange vegetables — carrot, red pepper, and a little sweet potato. The carotenoids are what deepen reds and oranges, and they work. Keep it as part of a balanced mix rather than a colour food in its own right, for the reason the label page gives: a food doing one job well often does the others worse.

The other homemade food

Worth mentioning because it is the same impulse pointed somewhere more useful: growing live food.

A jar of infusoria, a culture of microworms, a bottle hatching brine shrimp, an outdoor bucket of daphnia. These are genuinely valuable — live food triggers feeding responses that few other foods do, and newly hatched brine shrimp are a standard first food if you are ever raising fry. The live food page covers the cultures and the risks of collecting from the wild.

Is it worth it?

On cost, marginally and probably not. Ingredients come in quantities a few goldfish take months to eat, so a batch usually means buying more prawns than the fish will ever use. The costs page puts food low on the list of things worth optimising.

On quality, yes, as part of a varied diet — fresher, higher in real vegetable content, and often better taken than dry foods.

And when not to bother: a fish thriving on a good pellet does not need this. A household that will not handle raw seafood carefully should not do it. And a fish that is ill wants a complete formulated food, not an experiment.