FAQ: Grooming for fish

Clean the filter when the flow drops noticeably or the sponges clog, which is often every few weeks. Cleaning too often or too thoroughly removes the beneficial bacteria, so filters are cleaned gently.

The chlorine or chloramine in tap water and a big temperature difference can kill the nitrifying bacteria living in the sponges that break down ammonia. Rinse the sponges in a bucket of water taken from the tank.

Fill a bucket with tank water you would discard during a water change anyway and squeeze the sponge a few times until most of the dirt comes out. It does not need to be white again: a bit of brown remains because of the bacteria.

Replace a sponge when it cracks, crumbles, loses its shape or no longer springs back after rinsing. If the filter has several sponges, replace them one at a time a few weeks apart so the bacterial colony survives.

Most of the beneficial bacteria live in the filter media. Replacing it all at once leaves too few bacteria, so ammonia and nitrite, which are dangerous to fish, can rise suddenly.

Activated carbon becomes saturated and stops working within a few weeks, so it is replaced as the manufacturer advises. Many tanks do not need it all the time: it is mostly used to remove colour or odour and to absorb medication residue after treatment.

Sponges and wool trap dirt (mechanical filtration), ceramic rings and porous media house bacteria (biological), and activated carbon or resins absorb certain substances (chemical). Water usually passes through the mechanical stage first.

Fine filter wool is replaced most often, because it traps the smallest particles and clogs quickly, often every week or few weeks. Clogged wool reduces flow, and it holds relatively few beneficial bacteria.

Unplug the filter, remove the impeller cover and carefully pull the impeller out. Clean it and its chamber with a small brush and check the shaft and bearings for wear. A clean impeller runs quieter and stronger.

The usual causes are trapped air, a dirty or worn impeller and shaft, or vibration where the filter touches the glass or cabinet. Clean the impeller, bleed out the air and check how the filter is mounted.

Algae and slime build up inside the hoses and gradually reduce flow. Every few months switch off the filter, close the taps, disconnect the hoses and clean them with a long flexible hose brush.

Before switching on, the filter must be filled with water and the air bled out, usually with a built-in priming pump or button. Check that the sealing ring is seated properly, open the taps and watch for drips.

Yes. When cleaning the filter, wipe the ring and its groove and check it for cracks or thinning. Some manufacturers recommend greasing it with a special aquarium-safe lubricant, so follow the filter's instructions.

Switch the filter off and slip a container or bag under it before lifting it out, so the dirt does not spill into the tank. Rinse the sponges in tank water, clean the impeller and intake slots, then reassemble it.

Switching it off briefly, such as during cleaning, does the bacteria almost no harm. After a few hours without flow the filter runs short of oxygen and bacteria start to die. If it has been off for a long time, rinse it in tank water before restarting.

Each day it is worth checking the water temperature, that the filter and lights work, counting the fish and seeing that they behave normally. Feed in moderation and remove leftover food.

Every week or two you usually change part of the water while siphoning the substrate, clean the glass and remove dead plant leaves. It is also a good time to test the water and check the equipment.

Monthly, or as needed, the filter is gently cleaned, the fine wool replaced, the plants trimmed, and the lid and lighting wiped. It is worth checking the hoses, heater, cables and silicone seams too.

For a medium-sized tank, weekly maintenance with a water change and glass cleaning often takes about half an hour to an hour. With the right tools to hand and a settled routine, it goes faster.

No, a full clean-out removes the beneficial bacteria and the tank has to cycle again, which is dangerous for fish. Regular partial maintenance keeps a tank running for years. A full clean is only needed after serious disease or when replacing the tank.