FAQ: Tank Decor for fish

A black or dark blue background brings out fish and plant colours and creates a sense of depth. A light or frosted white background suits minimalist tanks, while photo backgrounds work better in tanks with few plants.

A 3D background looks natural and gives fish hiding places, but it takes up some of the water volume and dirt can collect behind it. Choose one made for aquariums that is firmly glued or sealed so fish cannot get behind it.

Fit a 3D background before filling the tank: trim it to size, rinse it and glue it to the back glass with aquarium-safe silicone, letting it cure completely. Leave openings for filter pipes and the heater.

You can paint the outside of the back glass, for example black or blue, but it is nearly permanent. Paint only the outside, while the tank is empty, and make sure no paint or fumes get inside.

Bubbles and marks appear when the film was applied to dirty glass, air was left behind or too little liquid was used, and over time moisture gets in. Peel the film off, clean the glass and reapply it with background adhesive fluid.

A background is not essential, but many fish feel calmer with no movement, light or reflections behind the tank. It also hides cables, the filter and the wall; without one, a tank viewed from both sides can work as a room divider.

Peel the film off slowly from a corner, and clean off leftover adhesive with warm water, a plastic scraper and, if needed, a mild adhesive remover on the outside of the glass only. Clean and degrease the glass before applying a new background.

A lit or coloured background can look striking, but bright light from behind tires some fish and encourages algae on the background. Choose soft light, run it on a timer and do not leave it on at night.

Natural rocks and wood look more alive and grow beneficial bacteria and biofilm, but some change water parameters. Artificial decorations are lighter, inert and easier to clean; the choice depends on the style and your fishes’ needs.

Resin or ceramic ornaments made for aquariums are safe as long as they have no sharp edges or narrow openings a fish could get stuck in. Check that the paint is not flaking, and rinse the ornament before adding it.

It is not advisable, because plastic toys and household ornaments can contain paint, metal parts or plasticisers that leach into the water. It is safer to choose only decorations made for aquariums, whose materials suit permanent immersion.

Glazed or unglazed ceramics made for aquariums are inert and heavy, so they do not tip over and last a long time. Avoid decorative ceramics with metallic glazes or paints not meant for permanent immersion.

Paint usually flakes off cheap decorations or ones not made for aquariums, and from scrubbing with a hard brush or strong cleaners. Remove a flaking decoration, because paint particles can be swallowed by fish and pollute the water.

Ornaments connected to an air pump, such as treasure chests or divers, add oxygen to the water and create movement. But strong bubbling bothers calm-water fish such as bettas and drives CO2 out of a planted tank.

Glowing decorations made for aquariums are usually made of safe materials, but they mostly glow only under blue or UV light. Bright light at night stops fish from resting, so keep such lighting on only briefly.

They can, if they have sharp edges, rough surfaces or narrow openings in which a fish gets stuck. Feel a decoration before adding it, judge the openings against your largest fish, and choose smooth decor for long-finned fish.

In a small tank choose smaller decorations and leave more open swimming room, as big pieces take up water volume. A large tank suits bigger rocks and roots that create several zones and hiding places.

It is not required, but surroundings that resemble the natural habitat often stress fish less: Amazon fish suit wood, leaves and dark substrate, African lake cichlids piles of rock. This is known as a biotope aquarium.

A hide should let the fish slip in easily and turn round, but not be too large, because many fish like to feel walls around their body. Choose the opening size for the adult fish, not the juvenile.

The usual advice is at least one hide per territorial or bottom-dwelling fish, plus a few extra so weaker fish have somewhere to retreat. Spread the hides around different parts of the tank rather than in one pile.