04 Aquarium
Aquascaping for goldfish
Aquascaping is built around fish that stay small, leave plants alone and never dig. Goldfish do the opposite of all three. The constraints are unusual enough to be interesting, and a goldfish tank designed around them can look very good.
Aquascaping as a hobby is built around a set of assumptions: small fish, fish that leave plants alone, fish that do not dig, and a tank where the layout is the point and the fish are the accent.
Goldfish violate every one of those. They are large, they graze, they dig constantly, and they need the open water that a dense layout removes.
The usual response is to conclude that goldfish tanks cannot be attractive. That is wrong, but the route to an attractive one runs through a different set of constraints rather than around them.
The five constraints
Everything on this page follows from these.
They eat soft plants. Not occasionally — as a matter of routine. Anything tender is food.
They dig. Sifting substrate and spitting it out is ordinary carp foraging, as the domestication page explains, and it means anything rooted in open substrate will be uprooted.
They need open water. A goldfish is a big active fish. The layout competes directly with the thing it most needs from the tank.
Fancies are fragile. Protruding eyes, trailing fins, poor manoeuvring. Hardscape that is merely interesting to a tetra can be an injury to a telescope.
They produce a great deal of waste. Which means the scape has to be something you can clean under, indefinitely.
Design the swimming lane first
A very useful discipline, and it inverts the usual order.
Start by deciding where the clear run is — a length of open water along the tank that a goldfish can cross at speed without turning. Then place everything else around it.
Done the other way round, hardscape goes in because it looks good, plants fill the gaps, and the open water is whatever happens to be left. That is how goldfish end up in tanks that are visually full and functionally small. The tank size guide sets out the volume; a scape can quietly undo a good part of it.
Long and open beats tall and busy. This is also why footprint matters more than height when choosing a tank.
Scaped around the clear run
- The clear run, decided first: open water along the tank that the fish can cross at speed without turning.
- Planting above the fish. Floating plants give green, shade and nitrate export that cannot be dug up, though goldfish may eat soft ones; expect to replace them. Leave part of the surface open.
- Hardscape placed around the run: large, smooth, stable, and with no gap a deep-bodied fish could push into.
- Plants tied on, not planted: anubias and java fern attached to wood or rock, out of reach of a digging fish.
- Room for the siphon around and behind the hardscape, and no dense low planting to trap waste.
Substrate
The substrate guide covers the safety question — gravel that can lodge in a goldfish’s mouth is the hazard. The scaping questions are different.
Sand suits them. They can sift it, which they enjoy and which is good for them, and fine, rounded sand is the usual choice for that reason. It shows waste clearly, which sounds like a drawback and is actually useful.
Bare bottom is a real option, not a compromise. See below.
Deep planted substrates are a poor fit. Nutrient-rich aquasoil exists to feed rooted plants, and rooted plants do not survive here. What you get instead is an expensive layer that goldfish excavate, clouding the water each time.
A sloped substrate will not stay sloped. Within a month it will be flat, because a goldfish redistributes it. Design for flat, or contain the slope behind hardscape that actually holds it.
Hardscape
The rules are specific and they are about the animal rather than the aesthetic.
Smooth. Run a fingertip over every edge. If it would catch a fingernail it can catch a fin or an eye.
No narrow gaps. This is the one people miss. A deep-bodied fancy can push into a gap between two stones or under an arch and fail to reverse out of it. Avoid crevices, tunnels and anything a fish could enter but not obviously leave.
Large and stable. Goldfish push things. Hardscape should be too heavy to move and stacked so that it cannot topple — and never stacked so that a fall could crack the base glass, which the placement page explains is the tank’s most vulnerable part.
Inert, unless you want the hardness. Limestone, marble and many pale rocks dissolve slowly and raise carbonate hardness. For goldfish that is often acceptable rather than harmful — they tolerate moderately hard water — but it is worth knowing you are doing it, and the pH, KH and GH page covers what it changes.
Wood is generally excellent: smooth, inert, and an anchor for plants. Soak it first, expect tannins to tint the water for a few weeks, and weigh it down until it sinks.
No painted ornaments, no sharp resin, nothing with small openings. The decorations page covers the rest.
Plants: attach, do not plant
The technique that makes a planted goldfish tank possible.
Rhizome plants tied or glued to hardscape have nothing in the substrate to uproot. A goldfish can push at an anubias on a piece of wood all day and achieve nothing. Planted in sand, the same plant is out within a week.
What survives:
| Plant | Why it works |
|---|---|
| Anubias | Leathery and tough, attached to hardscape |
| Java fern | The same, and tolerant of low light |
| Bolbitis and similar attached ferns | Tough, attached |
| Mosses on wood or stone | Grazed but persistent |
| Floating plants | Cannot be uprooted, but soft species are grazed |
| Vallisneria | Sometimes outgrows the grazing; gets uprooted |
| Cryptocorynes | Occasionally, in a quiet tank with a heavy root mass |
What becomes food: elodea, cabomba, most stem plants, and anything soft-leaved. That is not a failure — elodea is frequently recommended as goldfish food, and a bunch of it is a perfectly reasonable thing to add on purpose. It is simply a crop rather than a fixture, and it should be planned as one.
The plants guide has the fuller species list.
Put the planting above the fish
The most goldfish-specific idea on this page, and it solves several problems at once.
Floating plants — amazon frogbit, water lettuce, salvinia — sit at the surface where a goldfish cannot dig them up. Goldfish graze the soft ones, frogbit, water lettuce and duckweed among them, so treat floaters as a renewable crop and top them up. What they give you:
- Green in the tank without the uprooting.
- Shade, which suppresses algae and which goldfish appreciate.
- Nutrient export. Fast-growing floaters with access to atmospheric CO2 can take up nitrate faster than rooted plants in a goldfish tank.
- A calmer fish, since overhead cover reduces the exposed feeling of a brightly lit open tank.
Two cautions. Duckweed is hard to remove once it is in — it arrives on other plants and multiplies fast, so if you want it as a feed crop, grow it in a separate container and add a portion at a time. And floaters need surface movement to be modest, which has to be balanced against the aeration a goldfish tank wants; the aeration guide covers the trade.
Design for the siphon
The constraint that separates a goldfish scape from every other kind, and the one that decides how the tank looks in two years rather than two weeks.
Goldfish produce a lot of waste. If the layout has places you cannot get a siphon into, waste accumulates there permanently, and no amount of water changing fixes it.
So:
- Leave access around and behind hardscape.
- Avoid dense low planting, which traps detritus and cannot be cleaned through.
- Avoid carpets entirely — they are the worst case, and goldfish would destroy them anyway.
- Keep the floor reachable, which is another argument for a bare bottom or a thin sand layer.
- Do not build into the corners, which are where waste collects and where a siphon needs room.
The cleaning guide covers the routine; the scape decides whether that routine is possible.
Background, and hiding the equipment
Part of the scape rather than an afterthought, and both are easier to do before the tank is running.
A dark background does more for the look of a goldfish tank than almost anything inside it. Black is generally better than blue: it removes the wall, the cable runs and the room behind the tank from view, and it gives an orange fish something to be seen against. Matt black card taped to the outside costs nothing and is reversible; adhesive film is neater and harder to fit; paint on the outside glass is permanent and the cleanest result.
Substrate colour matters too. A brilliant white or very pale substrate under a strong light tends to leave a goldfish looking washed out, partly through contrast and partly because fish adjust their own pigmentation to their surroundings over days and weeks. Mid-tone or dark sand flatters them, and it hides waste less well — which is a genuine trade-off rather than a clear win, since seeing the waste is how you know to siphon it.
Equipment. The heater, the filter intake and the airline all have to go somewhere, and hiding them badly is how gaps get created.
- Put them at one end, together, behind a single piece of hardscape rather than distributed around the tank.
- Leave the gap open at the bottom so a siphon reaches behind, and so a fish that swims in can swim out.
- A heater needs a guard and needs water flowing past it, so do not bury it in a tight pocket.
- A filter intake needs clearance and a pre-filter sponge, which also protects fins — the filtration guide covers the intake question.
- Never wedge equipment between rocks, which is a gap with a heater in it.
Rescaping a tank that already has fish in it
Worth its own section, because a rescape is a bigger disturbance than it looks and people combine it with other disturbances.
Do not rescape and service the filter in the same week. Both disturb the bacterial colony; together they can produce a measurable ammonia reading in an established tank. Space them by a fortnight.
Disturbing deep substrate releases what has accumulated in it. An old sand or gravel bed that has never been vacuumed thoroughly holds a surprising quantity of organic matter, and stirring the whole thing at once clouds the water and puts a real load on the filter. If you are replacing substrate, do it in halves a couple of weeks apart, or remove it entirely and accept a clean start.
Leave the fish in for small changes, which is far less stressful than catching them. Take them out for anything involving moving large hardscape, draining the tank, or working for more than a few minutes — and move them properly, into a container of their own water, as the handling guide describes.
Test for a week afterwards. A rescape is a minor version of the cycling question, and a small nitrite reading three days later is the normal consequence of having disturbed everything at once.
Expect the fish to be unsettled for a day or two. A rearranged tank is an unfamiliar tank, and goldfish notice. Dim the light, feed lightly, and leave them to it.
Three layouts that work
The open-water scape. A thin sand bed, two or three large smooth stones or one good piece of wood placed off-centre, anubias and java fern attached to it, floating cover above, and two thirds of the tank left as clear water. The default recommendation, and the one that suits the fish best.
The bare-bottom functional scape. No substrate at all. One strong piece of hardscape, plants attached to it, perhaps a couple of potted plants that can be lifted out for cleaning. Looks far better than its reputation, siphons in seconds, and shows the fish rather than the furniture. Particularly good for fancies, which spend time on the bottom.
The planted thicket, accepting losses. A bank of vallisneria or elodea at one end, replanted as it is grazed and uprooted, treated as an ongoing crop. High maintenance, genuinely green, and clear about what is happening: you are growing plants for the fish to eat and enjoying them in the meantime.
What does not work
| Approach | Why not |
|---|---|
| Carpeting plants | Destroyed in days; traps waste; needs high light |
| Iwagumi and other minimal stone layouts | Built on carpets and fine gravel |
| Delicate stem plants | Food |
| CO2 injection and high light | Works against the oxygen margin goldfish need; feeds algae |
| Fine sharp hardscape — seiryu, dragon stone edges | Eyes and fins |
| Tall, narrow tanks | Wastes the dimension goldfish use |
| Sloped or terraced substrate | Flat within a month |
| Dense background planting | Nowhere for a siphon to go |
Lighting
Goldfish do not need a light. Plants do, and algae does too.
Which means the lighting decision in a goldfish tank is a balance rather than a maximisation: enough for anubias, java fern and floaters — all of which are low-light plants — and no more, because a tank with a heavy nutrient load and a strong light grows algae faster than it grows anything you chose. The lighting page covers duration and intensity; a modest light on a timer for six to eight hours suits this kind of scape.
What it will look like
Some expectation-setting, because the aesthetic is genuinely different.
A goldfish tank will not look like a competition aquascape. It will not have a carpet, a forest, or a sense of density. What it can have is space, a few strong shapes, green attached to wood and floating above, and a large handsome fish moving through open water — which is a perfectly good thing to look at, and arguably a truer one, since it shows the animal rather than burying it in scenery.
The layouts that fail are the ones designed for a different fish. The ones that work look, in the end, quite like the places goldfish came from: open water, a few solid objects, and cover overhead.
Frequently asked questions
Can you aquascape a goldfish tank at all?
Yes, but not the way the aquascaping hobby usually means it. Carpets, delicate stem plants, fine sharp hardscape and dense planting are all incompatible with a large fish that digs, grazes and needs room to swim. What works instead is spare: open water, a few large smooth shapes, tough plants attached to hardscape rather than rooted, and cover floating on the surface. It is a different aesthetic rather than a lesser one, and it suits the animal.
Which plants survive goldfish?
The leathery, the attached and the fast. Anubias and java fern are tough enough to be largely ignored and, crucially, are tied to wood or rock rather than planted, so they cannot be uprooted. Floating plants cannot be uprooted either, but goldfish graze soft species such as frogbit, water lettuce and duckweed, so treat them as a renewable crop. Vallisneria sometimes outgrows the grazing. Almost everything soft — elodea, cabomba, most stem plants — is food rather than decoration, which is fine if that is what you intended.
Why attach plants instead of planting them?
Because goldfish dig. Sifting through substrate is ordinary foraging behaviour for a carp, and anything with roots in that substrate comes up sooner or later, usually within days. A rhizome plant tied or glued to a piece of wood or stone has nothing to uproot — the fish can push at it and nothing happens. It is the single technique that makes a planted goldfish tank possible.
Is a bare-bottom goldfish tank a legitimate design?
Very much so, and it is underrated. No substrate means no uprooting, no trapped waste, a floor you can siphon completely in seconds, and a clear view of what the fish are producing. Combined with one good piece of hardscape and plants attached to it, it looks considerably better than people expect — and it removes most of the maintenance burden that makes goldfish tanks look tired after a year.
What hardscape is safe with fancy goldfish?
Smooth, large, stable and gap-free. Protruding eyes and trailing fins damage on sharp edges, and a deep-bodied fancy can wedge itself in a narrow gap between stones and not get out. Choose rounded pieces, check every edge with a fingertip, avoid arches and crevices a fish could enter, and make sure nothing can be pushed over — goldfish move things. A beautiful layout that costs a telescope its eye is a failed layout.
Can I run CO2 injection on a goldfish tank?
It is a poor fit. CO2 injection exists to drive fast plant growth under high light, and goldfish are large, heavy-waste fish with less oxygen margin than most aquarium species — adding dissolved CO2 works against exactly the thing they need most. High light plus heavy nutrients plus a fish that eats plants is also a reliable recipe for algae. A goldfish tank is a low-tech tank by nature, and the plants that suit it do not need the help.
How do I stop goldfish destroying the layout?
Mostly by designing something they cannot destroy. Attach the plants, use hardscape too large to move, skip anything rooted in open substrate, and accept that a sloped substrate will be flat within a month. Where you want soft plants, treat them as a crop to be replaced rather than as a fixture. Fighting the behaviour does not work; the digging and grazing are foraging, not vandalism, and they will not stop.
Does the scape need to leave much open water?
More than a typical aquascape, and it is the constraint people get wrong most often. A goldfish is a large, active fish that needs a length of clear water to swim in, and a layout that fills the tank has removed the single thing the animal most needs from it. A reasonable discipline is to design the swimming lane first — a clear run along the length of the tank — and then place everything else around it rather than the other way round.