FAQ: Filters for fish

The filter should run all the time, because its bacteria need a constant flow of water and oxygen, so it should not be switched off by a timer. Timers suit the lighting, and the air pump or CO2 only if it fits the tank's needs.

A filter's and air pump's power draw is usually modest and is shown in watts on the box. The heater uses the most, especially in a cold room, so a lid, a spot away from the window and a correctly sized heater help save energy.

Ponds use dedicated pressurised or gravity filters with a pump, often with a UV lamp. They are chosen by pond volume and fish stocking, and koi need much more powerful filtration than a few goldfish.

In cold climates the pond filter and pump are often switched off, cleaned and stored frost-free, with the pump kept in a bucket of water so the seals do not dry out. To keep oxygen reaching the fish, an ice preventer or aerator stops the whole surface freezing over.

Aquarium filters are usually not designed for outdoor conditions, sun and frost, and their capacity is too small for a large pond. For a small tub or balcony pond one sometimes works, but then use electrical connections rated for outdoor use.

Clean the filter at least a week before the trip, not on the last day, so the bacteria can recover, and check everything runs smoothly. Ask whoever looks after the tank to check daily that the filter and heater are running and the water level has not dropped.

Transport the filter media in a sealed container of tank water so it does not dry out, and keep it from getting too cold or hot. On arrival restart the filter as soon as possible, then feed lightly for the first few days and test ammonia and nitrite.

Planted tanks often get an external filter, as its flow spreads nutrients and CO2 evenly and the pipes take up little space. The filter should not churn the surface too much, since that drives off CO2.

They are clear glass or acrylic intake and outlet pipes for an external filter that are barely visible in the tank. They are popular in planted aquariums for their looks, but they are fragile and need regular cleaning with special brushes.

An outlet that gently ripples the surface improves gas exchange and oxygen levels. If the surface is churned too hard, CO2 is lost and the water gets noisy, so set the outlet so the surface just ripples.

Splashing and extra evaporation come from an outlet that sits too high, a hang-on filter's waterfall or a low water level. Raise the water level or lower the outlet, and a lid also helps cut both evaporation and splashes on equipment.

After treatment a larger water change and adding activated carbon to the filter to remove medication residues are often advised, if the medication's instructions say so. Do not swap out the biological media straight away, but keep an eye on ammonia and nitrite.

A spare sponge or sponge filter can be kept running in the main tank so it is always colonised with bacteria. When a quarantine or treatment tank is needed, you move it over and that tank has a working biological filter straight away.

A quarantine tank usually gets a simple sponge filter that is easy to clean or disinfect and does not interfere with treatment. Ideally it is pre-matured in the main tank and cleaned thoroughly after use.

No, the filter must run at night too, since the bacteria start to suffocate when it is off and the fish need oxygen. If it keeps you awake, try cleaning it, replacing the impeller, placing it on a soft base or choosing a quieter model.

Check the tank volume the filter is rated for, its flow and whether it can be adjusted, how much media it holds, how easy it is to clean and whether spare parts are available. How much space it takes in the tank or cabinet also matters.

zoogidas.lt compares prices from Lithuanian online pet shops, so you can see the same filter at several shops in one place. The site itself sells nothing – you buy the filter on the chosen shop's website.

The product page on zoogidas.lt shows price history, so you can see whether a filter's or heater's price is now higher or lower than before. This helps you decide whether to buy now or wait.

Prices are collected about daily, and each product shows when its price was last checked. Always confirm the final price and stock on the shop's website before buying.

Biological and chemical media are often sold in packs of different volumes, so it pays to compare the price per litre. On zoogidas.lt you can compare products by price per kilogram or litre, which makes it easier to see which pack is really cheaper.