Equipment
The filter has started rattling and humming
A filter that changed its noise overnight is telling you about air, the impeller, or something touching something else. None of these need a new filter. Unplug it before you touch it, then go through the three in order — most cases are solved in under ten minutes without buying anything.
Watch it
Test these first
Before anything goes into the tank and before anything comes out of it, get these numbers. They cost fifteen minutes and they decide everything that follows.
- Ammonia — total ammonia — the ammonium ion plus free ammonia, added together
- Temperature — the temperature of the water itself — not of the room the tank sits in
What is usually behind it
| Cause | How to confirm | Time to resolve |
|---|---|---|
| Water level too low, so the intake is drawing air | The noise is a sucking or gurgling rather than a rattle, and it is worse when the tank has evaporated down. Topping the level up quiets it immediately. | Immediate once the level is restored |
| Air trapped in the pump housing after maintenance | The noise started right after a water change or a media clean, and the unit runs quietly for a moment after being tilted. | Minutes |
| Debris or wear in the impeller | A hard rattle or a grinding note, often with reduced flow. Unplug, remove the impeller and inspect the blades, the shaft and the rubber bushings. | Twenty minutes, or a few days if a replacement part is needed |
| Vibration transmitted into the tank or cabinet | The noise is a hum rather than a rattle and changes when you place a hand on the filter body or the tank rim. A hang-on-back unit resting against a wall or a lid is a common culprit. | Immediate |
Water level too low, so the intake is drawing air
How to confirmThe noise is a sucking or gurgling rather than a rattle, and it is worse when the tank has evaporated down. Topping the level up quiets it immediately.
What to doTop up with treated water and keep the level within the range the filter expects. A tank in a dry room can lose a surprising amount in a week, which is the one genuine use for knowing your room humidity.
Time to resolve: Immediate once the level is restored
Air trapped in the pump housing after maintenance
How to confirmThe noise started right after a water change or a media clean, and the unit runs quietly for a moment after being tilted.
What to doUnplug it, tilt the housing to release the bubble, and restart. If it returns each time, check the seals and lid seating — a housing that does not close properly keeps drawing air in.
Time to resolve: Minutes
Debris or wear in the impeller
How to confirmA hard rattle or a grinding note, often with reduced flow. Unplug, remove the impeller and inspect the blades, the shaft and the rubber bushings.
What to doClean it with a soft brush and reseat it carefully. Replace the impeller or its shaft if either is chipped, worn or bent — those are ordinary wear parts and the manufacturer sells them.
Time to resolve: Twenty minutes, or a few days if a replacement part is needed
Vibration transmitted into the tank or cabinet
How to confirmThe noise is a hum rather than a rattle and changes when you place a hand on the filter body or the tank rim. A hang-on-back unit resting against a wall or a lid is a common culprit.
What to doReseat the unit so nothing touches it, and put a strip of foam or a piece of aquarium sponge between the filter body and the rim. Move the tank a finger's width off the wall if the cabinet is resonating.
Time to resolve: Immediate
What not to do
These are the moves that make this particular problem worse, and they are all common. Most of them come from wanting to do something substantial when the right answer is something small.
- Do not open or reach into a filter that is still plugged in. Unplug it at the outlet first — this one is about you, not the fish.
- Do not silence a rattle by wedging the impeller with anything. If it is fouled, clean it; if it is worn, replace it.
- Do not lubricate any part of an aquarium filter with household oil or grease.
- Do not run a hang-on-back unit at a low water level for weeks because the noise is tolerable. It is drawing air and working the impeller dry.
Keeping it from coming back
Noise is nearly always maintenance arriving late. Keep the water level topped up with treated water, clear the intake and squeeze the mechanical media at every water change, and take the impeller out to clean it every couple of months as routine rather than as a response. Seat the filter so it touches nothing but its own bracket, and keep the manufacturer instructions where you can find them so you know which parts on your model are meant to be replaced.
Reference for this page
Parameters
Equipment involved
- Filtersturning water over and housing the bacteria
- Filter Media & Cartridgeswhat actually does the filtering, and when it gets replaced
- Room Temperature & Humidity Monitorswatching the room the tank lives in
Related problems
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Published sources
- Electrical Safety Foundation International
- US Consumer Product Safety Commission — Safety Education
- USGS Water Science School — Dissolved Oxygen and Water
Published figures on this page come from the documents above. Where a value depends on species, pH or temperature, that is stated rather than averaged into a single number.