FAQ: Filters for fish

A well-maintained filter often lasts many years, with the impeller, its shaft and the seals wearing most, and these can be replaced. It is time for a new filter when the motor runs hot, noise persists after cleaning or parts are no longer available.

Heaters can last several years, but their thermostats can drift over time. Since a failure can overheat or chill the water, check the temperature daily and replace an ageing heater promptly, especially if its glass is cracked.

A used filter can be a good choice if it runs quietly, has no cracks and spare parts are available. Clean it thoroughly and replace the media before use, and check a used heater especially carefully, as its failure is more dangerous.

External filters are usually quieter because the motor sits in the cabinet, as are sponge filters with a quiet air pump. A manufacturer's noise rating in decibels, rubber mounts and an outlet that does not splash also help.

Cartridge filters are simple: pull out the cartridge and put in a new one, but you throw out some bacteria each time and depend on that model's cartridges. Filters with loose media let you choose and combine media yourself, and the biological media last a long time.

If an external filter's hose comes loose below the tank, it can siphon the aquarium down to the intake level. Secure the fittings firmly, use the taps, do not set the intake deeper than needed and check for leaks after each cleaning.

Clear pipes and hoses that get light quickly grow algae and slime, especially when the water is rich in nutrients. Clean them regularly with a brush, and dark-coloured hoses and moderate lighting slow this down.

Small snails often move into the filter and are mostly harmless, since they feed on debris. They can get into the impeller and jam it, though, so a sponge over the intake helps, and you can pick them out when cleaning the filter.

Yes, but the intake should sit higher off the bottom or have a sponge on it, because sucked-in sand scratches and wears the impeller and its shaft. Also make sure the filter's current does not stir the sand off the bottom.

Inspect the seal every time you clean the filter: if it has hardened, cracked or stretched, it is time to replace it. Greasing it with the lubricant the manufacturer recommends keeps it supple longer and helps prevent leaks.

Axolotls like cool, calm water, and strong current stresses them. A sponge filter or an external filter with a spray bar and reduced flow is usual, and they normally do not need a heater.

Discus need very clean, warm water, usually around 28–30 °C, and calm flow. Strong biological filters with a gentle outlet and a reliable heater are used, and the water is changed often.

In small round bowls the water fouls quickly, so without a filter and frequent water changes fish struggle there. If you use one, a small sponge filter fits, but most fish are better off in a rectangular tank with a normal filter.

A protein skimmer injects lots of fine air bubbles into the water; organic matter sticks to them and collects as foam, which is gathered in a cup. It is used in marine aquariums and works poorly in fresh water.

In a trickle filter water drips through media that is not fully submerged, so the bacteria get plenty of oxygen and break down ammonia very efficiently. They are often built into top filters or sumps, and bio balls suit them.

Yes, some external and internal filters have a built-in heating element, so no separate heater is needed in the tank. It saves space, but if one part fails you may have to replace the whole unit, and the temperature still needs checking with a thermometer.

For most aquatic turtle species the water is kept at about 24–28 °C, though the exact range depends on the species. A heater with a protective guard or an external inline heater is used so the turtle cannot break it.

Many popular freshwater shrimp do well at room temperature, around 20–25 °C, so a heater is often unnecessary. It helps in cool rooms to prevent swings, since shrimp are sensitive to sudden changes.

Yes, as long as the heater is fully submerged and does not touch the sides or bottom, since a hot surface can deform plastic. Use a guarded heater of suitable wattage, especially in small quarantine or transport containers.

Push the hoses fully onto the fittings and add hose clamps if needed. At the tank rim, fix them with the manufacturer's holders so the pipes do not move, and avoid sharp bends that pull the hose off its fitting.