Safe aquarium decorations for goldfish

Goldfish explore with their mouths, push things around, dig, and bump into whatever is in front of them. Several breeds have been selected for features that make this risky: eyes on stalks, fluid-filled sacs, fins longer than their bodies. So decor for a goldfish tank is chosen on different rules from a community tank. Almost anything can go in, as long as it passes three tests: is it smooth, is it stable, and is it inert. The rest is taste.

Smooth over sharp

Run a nylon stocking over any ornament before it goes in. If it snags the fabric, it will snag a fin. That test catches the moulding seams on cheap resin castles, the rough edges of some slate and the sharp facets of lava rock, all of which routinely cause torn fins that then invite infection.

For some breeds the stakes are higher. A telescope or black moor carries its eyes on protruding stalks; a bubble eye has delicate fluid sacs below the eyes that can tear on a stone; a celestial’s sight is unreliable, since the retina of the strain studied degenerates in the first months. Orandas trail a hood and long fins, ryukins and fantails have finnage that folds around obstacles. For these fish, smooth is not a preference. Rounded river stones, glazed ceramics, soft silk plants and driftwood with no splinters are the working materials.

No holes a fish can push into

Goldfish grow, and they push head-first into openings that look far too small. A tunnel a young fish swims through happily is a trap for the same fish a year later, and a wedged goldfish can die within hours in a tank you are not watching. Check every hollow ornament, castle, log and cave for openings between roughly the width of a fish’s head and its body. Either block them permanently with aquarium-safe silicone or leave the item out. Anything a goldfish uses as a hide should have openings so wide that it could never get stuck: an arch rather than a hole, a ledge rather than a tunnel.

Materials that are safe

Inert rock. Slate, granite, quartz, basalt and smooth river cobbles do not change water chemistry. Drop a little vinegar on a dry rock: fizzing means it contains carbonate and will raise hardness and pH.

Driftwood. Sold as bogwood, mopani, spider wood and other names, driftwood is safe once it has been soaked. It releases tannins that tint the water tea-coloured and nudge pH slightly downward, which is harmless and fades over months. Boil small pieces or soak large ones for a week or two so they sink and release the worst of the colour.

Ceramics and glass. Glazed ceramic ornaments, unglazed terracotta pots and glass pieces are inert and easy to clean. Avoid anything with a crazed or flaking glaze.

Resin ornaments made for aquariums. Quality resin is inert and comes in every style. Inspect the edges for sharp moulding flash, and skip any piece that smells strongly of chemicals when dry.

Plants, real or silk, are decor too, and soft-leaved silk is kinder to fins than stiff plastic. Our guide to plants for goldfish tanks covers the species that survive a goldfish.

Moving and air-driven ornaments

The bubbling treasure chest, the spinning wheel, the diver with a stream of air. A fair assessment, since they are a whole aisle.

They are not harmful in themselves. The air is being delivered by an ordinary air pump, and the surface agitation it produces is genuinely useful — aeration and oxygen covers why that is the part that matters rather than the bubbles.

The objections are practical. Moving parts are one more thing to fail and one more place for a fin to catch. The hinges and gaps on a chest are exactly the openings this page is otherwise about. They collect debris in places a siphon cannot reach. And the pump running one of these is doing less useful work than the same pump driving a sponge filter, which aerates and filters — the filtration guide makes that case.

Coloured lights built into ornaments are for the viewer. They do nothing for the fish, and a long day of bright light grows algae.

So: not a hazard, not a priority, and if you like them, run a sponge filter off the same pump as well.

What to avoid

Painted items not sold for aquariums, whose coatings can flake or leach. Copper, brass and galvanised zinc, which are toxic to fish, and anything that rusts. Shells, coral, limestone and marble, which dissolve slowly and push hardness and pH upward; that can be useful in very soft water, but only if you intend it and are testing for it. Small gravel, which keepers report lodging in a goldfish’s mouth or throat, as the substrate guide explains. Sharp lava rock, dragon stone and splintery wood. And aquarium-safe labels taken as a guarantee: the label is the maker’s claim about the material, and says nothing about whether its shape is safe for a slow fish with fragile eyes.

Testing something you are not sure about

Four checks, none of which needs anything you do not have, and between them they catch the usual problems.

1. The stocking test. Run a nylon stocking or a pair of tights slowly over every surface. If it snags, a fin will snag. This finds moulding seams and edges that fingers miss entirely, because skin is far less delicate than a fin membrane — the torn fins page uses the same test for finding what has been tearing them.
2. The vinegar test. A drop of household vinegar on a dry spot. Fizzing means carbonate, which means the item will slowly raise hardness and pH. That is occasionally useful in very soft water and is otherwise an uncontrolled change — pH, KH and GH covers doing it deliberately instead.
3. The smell test. Dry, at room temperature. Anything strongly chemical, solvent-like or plasticky goes back.
4. The bucket test, for anything you still want to use. Put it in a bucket of tap water for a week alongside a second bucket of the same water with nothing in it, and test both for pH and hardness at the end. If the readings match, the item is not changing pH or hardness; that does not test for toxins, so this slower check settles only the carbonate question.

And the fifth question, which is not a test: could a fish get into it, or behind it where you cannot see? That one is answered by looking, and it is the one that matters most as the fish grow.

Household objects, item by item

People put all sorts of things in aquariums, and the answer varies by object rather than by category.

• Glazed ceramic mugs and bowls: generally fine if the glaze is intact and food-safe, and if the opening is wide. Check for crazing — fine cracks in the glaze — which lets water into the body beneath.
• Unglazed terracotta pots: excellent, cheap and much used. A pot on its side with a wide mouth is a good refuge; a drainage hole that a growing fish could wedge into is not, so block it or face it into the substrate.
• Glass bottles and jars: the classic mistake. A fish that swims in at four centimetres does not swim out at eight, and a bottle is also impossible to see into properly. Leave them out.
• Marbles and glass beads: no, and the substrate page explains why: they are loose pieces that a goldfish mouths like gravel, and they can lodge in the same way.
• Plastic toys: depends entirely on the plastic, the paint and the shape, and there is no way to know about the first two. The ones made for aquariums cost very little.
• Seashells and coral from a holiday: they raise hardness continuously and broken edges are sharp. Ornamental rather than useful.
• Coins: many contain copper, brass or zinc, so no.
• PVC pipe: genuinely good, and what many breeders use. Inert, cheap, and a wide length of it makes a refuge with no trap in it. It looks industrial, which is what plants and stone are for.
• Slate and stone from a garden centre: usually fine after the vinegar test and a scrub, and often far cheaper than the same rock sold for aquariums.

Used decor, and decor from another tank

A short section with one principle: dry it.

Ornaments, rocks and wood from another aquarium can carry parasites, their eggs, and bacteria, in exactly the way a plant or a fish can — and almost nobody thinks of decor as a route in. The quarantine page covers the same reasoning applied to everything else.

What works:

• Scrub in plain water, with a brush kept for the tank.
• Then dry it completely, somewhere warm, for a couple of weeks as a keepers’ rule of thumb. The Merck Veterinary Manual advises storing aquarium equipment dry, and drying costs nothing.
• A bleach soak is the faster option some keepers use for hard, non-porous items, but no cited strength or contact time is available here, so none is given. If in doubt, dry it for longer or replace it.

What does not work is a rinse and straight in, which is how a tank acquires a problem from a second-hand ornament bought in good faith.

Porous items — wood especially — hold more and dry more slowly. Give wood longer, or replace it, since a piece of bogwood is not expensive.

Backgrounds

The cheapest single improvement to how a goldfish tank looks, and it does something for the fish too.

What it does. A background hides cables, filter bodies and wall, which is most of what makes a tank look unfinished. It also gives the fish a solid visual boundary rather than a transparent one, and goldfish generally settle better against a dark backdrop than against a bright reflective one.

And it changes the fish’s colour. Goldfish pale against bright, bare surroundings and deepen against dark ones, which is the same mechanism behind pale or faded colour and is a faster lever than any colour food.

The options, cheapest first: matt black or dark blue card taped outside the back glass; a roll of aquarium background film applied wet with a squeegee; matt paint applied directly to the outside of the back pane, which is permanent and looks best; or a rigid moulded 3D background inside the tank, which looks striking, reduces the swimming volume noticeably, and creates gaps behind it that are both a trap and impossible to clean. For goldfish specifically, the first three are the sensible ones.

Fit it outside the glass. Anything inside is one more surface to clean and one more place for waste to collect.

Preparing new decor

Rinse everything in hot tap water and scrub with a brush kept for the aquarium; no soap, ever, because residues cling and end up on gills. Soak driftwood until it sinks and the water stays reasonably clear between changes. Give rocks the vinegar test and a good scrub for any soil or algae. Resin and ceramics need only a rinse. There is no need to quarantine dry items, but anything that has been in another aquarium should be treated as possibly carrying parasites and either dried for a couple of weeks (a rule of thumb) or scrubbed and rinsed thoroughly before it joins your fish.

How goldfish actually use decor

Watch a goldfish for an hour and you will see it mouth every surface, graze the film on rocks and leaves, root through the substrate, and rest at night in the same favoured spot, often in the shelter of a plant or beside a large stone. They are not cave-dwellers and do not need dark hides, but a tank with nowhere to shelter is a tank where a startled fish has nowhere to go. One or two broad, open refuges, a clump of plants or a smooth arch, gives them a choice. They also rearrange things: light ornaments end up wherever the fish decide, and a large fish can move a surprising amount of sand.

Re-check it as the fish grow

The one maintenance job for decor, and it takes two minutes.

The fish changed and the ornament did not. An opening a juvenile passed through freely becomes a tight fit at eight centimetres and a genuine trap at twelve. This is a common way a long-standing, apparently safe ornament turns into an emergency, and it happens quietly.

Once a year, during a water change, check:

• Every opening, against the fish as they are now rather than as they were.
• Chips and cracks in resin, which expose a sharp edge under a smooth surface.
• Crazed or flaking glaze on ceramics.
• Silicone joints on anything you bonded, which can let go over years.
• Stacked rock, which settles as the substrate beneath it shifts — goldfish dig, and a stone that was stable on day one may not be on day four hundred.
• Behind and under everything, which is where debris accumulates and where a fish that has not been seen for a few days sometimes turns out to be.

And if a fish has grown past an ornament’s openings, the answer is to remove the ornament rather than to hope. It is a cheap object and the fish is not.

The minimalist approach

Goldfish are big, active animals that need open water more than ornaments. The layout that suits them best is the one aquascapers call negative space: a clear foreground for swimming, decor toward the back and sides, and a few large pieces rather than many small ones. It looks calmer, it is far quicker to keep clean, as the cleaning guide shows, and it makes it easy to see all of your fish at once, which is the first step in noticing when one is unwell. Remember that decor displaces water: a tank packed with rock holds noticeably less than its nominal volume, and the aquarium volume calculator lets you allow for it. For a picture of how all of this fits together, our ideal goldfish aquarium guide walks through a complete layout, and aquascaping for goldfish covers the design problem itself — why plants have to be attached rather than planted, and why the gaps in a layout matter more than its edges.