FAQ: Tank Decor for fish

Build caves from flat rocks such as slate, set on the bottom glass so the top stones rest on solid lower ones. Leave several entrances so a dominant fish cannot trap another, and check the structure is stable.

Hard, dried wood sold for aquariums suits an aquarium: mopani, mangrove roots, spiderwood, Malaysian driftwood and similar. It decays slowly, lasts a long time and is usually prepared so it has no bark or resin.

Scrub the wood with a brush, scald it with hot water and soak it in a bucket for days or weeks, changing the water. That way it soaks up water and stops floating, and some of the tannins that tint the water are released.

Dry wood is full of air, so it floats at first until it soaks up water. Soak it longer, weigh it down with a rock, or fix it to a flat stone or slab buried in the substrate.

Wood releases tannins that tint the water amber, like tea. They do not harm fish and even lower pH slightly; the colour can be reduced by pre-soaking the wood, changing water and using activated carbon in the filter.

Many soft-water fish such as tetras, bettas or discus live in dark, tannin-stained water in the wild, so it resembles their natural environment. Tannins lower pH and hardness slightly, but they do not cure health problems.

A white or greyish slimy coating on new wood is usually a harmless fungus or bacterial film that disappears within a few weeks. It can be wiped off, and snails, shrimp and some fish happily eat it.

Only hard, completely dry and dead wood without bark, mould or rot, such as oak, beech or fruit trees. Conifer wood is unsuitable because of its resin, and any branch you find must be scrubbed, scalded and soaked for a long time.

Conifers such as pine, spruce or fir are unsuitable because of their resin, as is soft, fast-rotting wood and painted, varnished or treated wood. Also avoid trees whose sap or leaves may be toxic.

Mopani wood is very hard, heavy and two-toned, usually sinks straight away but releases tannins for a long time. Mangrove roots are branchier and lighter, so they often need longer soaking before they stop floating.

Spiderwood is branchy decorative wood with thin twigs that looks like a tangle of tree roots. It is light, so it floats for a long time, and harmless white fungus often appears on it at first.

Wood matters to many suckermouth catfish, especially bristlenose plecos and panaques: they rasp it for fibre, and biofilm grows on it. In a tank with these catfish it is advisable to have at least one piece of hardwood.

Hard aquarium wood can last many years, but it slowly softens and breaks down, especially if catfish rasp it. When the wood becomes soft, crumbly or starts to rot, it is best replaced so it does not foul the water.

Yes, wood releases tannins and humic acids that lower pH and carbonate hardness slightly, especially in soft water. In hard water the effect is small, but in a tank with shrimp or sensitive fish it is worth watching the parameters.

Driftwood can be screwed with a stainless steel screw onto a flat stone or acrylic slab buried in the substrate, or weighed down with rocks. It can also be glued to another decoration with aquarium-safe glue.

Dried, untreated bamboo is used for decorations or hides, but it softens over time and can rot. Do not use varnished or painted bamboo, and check hollow canes regularly for debris building up inside.

Indian almond or oak leaves are added to aquariums as natural decor and a source of tannins, especially for bettas, shrimp and soft-water fish. They tint the water and slowly break down, so replace them once they go soft.

Alder cones and some nut shells, such as coconut, are used in aquariums as hides and a source of tannins. They must be clean, untreated, well scalded and free of mould, and any that start rotting should be removed.

There are film backgrounds with photos or a plain colour that are stuck or fixed to the outside of the back glass, and 3D backgrounds of foam or resin fitted inside the tank. A dark plain background also hides cables and the wall behind the tank.

Clean and degrease the outside of the back glass, spray it with water and a drop of detergent or a special background adhesive, and lay the film on. Push the bubbles out from the centre to the edges with a rubber squeegee or plastic card.