FAQ: Supplies for fish

Salinity is usually measured with a refractometer or hydrometer and typically kept at a specific gravity of about 1.024–1.026. Salt stays behind when water evaporates, so top up with fresh rather than salt water.

Hardy species are often suggested for beginners, such as captive-bred clownfish, some gobies or Banggai cardinalfish. Captive-bred fish adapt more easily and accept food sooner.

Yes, most corals live in symbiosis with algae that need strong light of the right spectrum. LED lights made for marine tanks let you set the intensity and colour to suit the type of coral.

A marine tank usually takes longer to settle than a freshwater one – several weeks or more, especially with dry rock. Hardy animals go in first, and corals and more sensitive fish only once the water has stabilised.

Most fish do well on a good-quality staple dry food supplemented with frozen or live food. Choose food by whether the fish feed at the surface, mid-water or on the bottom, and whether they are carnivores or herbivores.

Uneaten food and a lot of waste quickly raise ammonia and nitrate levels and encourage algae and cloudiness. Fish act hungry even when full, so it is better to feed smaller portions.

Most often fish are added to an uncycled tank, too many or incompatible fish are bought, and the filter is rinsed in tap water. A tank that is too small and skipped regular water changes are also common.

Algae grows when there is too much light and too many nutrients, for example from overfeeding or infrequent water changes. A little algae is normal, and shorter lighting, live plants and moderate feeding help keep it down.

A brown film on the glass and decor in a new tank is usually diatoms, which thrive on silicates in the water. They normally disappear on their own once the tank settles and wipe off easily.

A yellowish tint is often caused by tannins from driftwood or a build-up of organic matter. Tannins do not harm fish, and water changes and activated carbon in the filter reduce the tint.

A healthy tank smells earthy, while a rotten or sulphur smell means food, plants or a dead fish are rotting somewhere or sludge is building up in the substrate. Find and remove the cause, clean the substrate and change some water.

A surface film is usually made of proteins and fats from food plus bacteria, especially when the surface barely moves. A filter outlet that agitates the surface, a surface skimmer and lighter feeding help.

A filter often hums because of trapped air, a clogged impeller or a low water level, while an air pump vibrates when it stands on a hard surface. Clean the impeller, top up the water and put the pump on a soft base or hang it up.

CO2 injection is mainly needed for densely planted tanks with strong lighting and fast-growing plants. A simple tank with undemanding plants does not need it, and incorrectly dosed CO2 can harm fish.

River fish such as some danios or barbs like stronger flow, while bettas, gouramis and fancy goldfish prefer calm water. Flow can be reduced by pointing the filter outlet at the glass or using a spray bar.

A background is optional, but it hides cables and the wall, makes the tank look better and helps some fish feel secure. A dark background often brings out the fish’s colours.

Yes, if the sound of the filter or air pump and the light do not bother you. Choose a quiet filter, control the lighting with a timer, and put the air pump on a soft base or do without it.

A child is better off with a tank that is not too small, around 40–60 litres, with a few hardy fish such as livebearers. An adult should still be responsible for the care, while the child can help feed and watch the fish.

A paludarium is a tank that combines a water section and a land section, so both aquatic and land plants can be grown in it. It can house fish, shrimp or amphibians, but it is more complex to set up than an ordinary aquarium.

It is the art of arranging an aquarium with plants, rocks and wood so that it resembles a natural landscape. Such tanks usually need stronger lighting, nutrient-rich substrate and CO2.