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Canister filter leaking from the seal, hose, or body

Updated: 23 October 2026

Water is on the cabinet floor, or it is beading at the motor head, and the socket is closer than you would like. A canister filter leaking is a place-of-drip problem after it is running: seal, hose, or a cracked body, once the power is safe. The notes come from the Fluval 07 manual, All Pond Solutions’ UK leak note, and amazon.co.uk reviews from 20 October 2026. A qualifying purchase from the [canister filter comparison](/hub/diy-supplies/canister-filter) can earn a commission at no extra cost to you. The first prime is [how to set up a canister filter](/hub/diy-supplies/canister-filter/sub/canister-filter-how-to-set-up). Choosing a model is the [canister filter buying guide](/hub/diy-supplies/canister-filter/sub/canister-filter-buying-guide), and the 60–220 litre pick is [best canister filter](/hub/diy-supplies/canister-filter/sub/canister-filter-best).

Water is on the cabinet floor, or it is beading at the motor head, and the socket is closer than you would like.

Our top picks

Fluval Fluval 207 external filter

Best overall

Fluval Fluval 207 external filter
9.2/10about £124.99
View offer
Fluval Fluval 307 external filter

Alternative

Fluval Fluval 307 external filter
9.0/10about £159.99
View offer
Hidom Hidom EX-1200 canister filter

Rank 3

Hidom Hidom EX-1200 canister filter
8.2/10about £64.94
View offer
On this page
  1. 1.Make the leak safe before you open the filter
  2. 2.Seal at the motor head
  3. 3.Hoses, valves, and shut-off
  4. 4.A crack is not a seal you can grease
  5. 5.What a single review does not prove

Make the leak safe before you open the filter

Find out whether the plug and the socket are dry before you touch either of them. If they are dry, switch the filter off at the plug, shut any valve you have, and catch the water. Fluval’s 207 bullets name AquaStop valves, so those hoses can be closed before the head comes off. The two unbranded listings state a valve cut-off for cleaning. If the plug or the socket is already wet, do not pull that plug by hand. Isolate the circuit at the fuse or the breaker, then unplug. A damaged cable or plug is the same stop. Filing a Schuko plug to fit a UK socket is outside these sources. Oase’s instructions add a drip loop so water on the cable does not run into the socket. Look for the joint only when the power is isolated and the drip has somewhere to go.

Seal at the motor head

Fluval’s 07 FAQ says a leak near the motor-head clamps is most likely the canister O-ring. Clean it, seat it fully in the channel, and use Fluval silicone lubricant A325. Do not use Vaseline or vegetable oil. The gasket should be moist, the cover in its only orientation, and the lift-lock clamps fully closed. A Fluval 107 review describes a silicone seal fitted the wrong way on the first install. All Pond Solutions’ UK note uses the same order for its own filter: see whether the water is at the top, the bottom, or the pipework, then check the motor-head O-ring and the hose adaptors. If the head joint is dry, look at the hoses next.
Fluval Fluval 207 external filter

Testsieger

Fluval Fluval 207 external filter
9.2/10about £124.99
View offer

Hoses, valves, and shut-off

A dry motor head sends you to the pipework. Connectors, the seals inside them, and a kinked hose are the usual places a drip reappears after a clean. Shut the AquaStop, or the valve cut-off the unbranded listing states, so the tank does not siphon onto the floor while the hose is off. One of ten reviews on the 1,800 L/h unbranded canister, ASIN B0GRMZD273, says the unit leaked on first setup and would not pump. If the hoses are dry and water is still leaving the canister wall, you are no longer looking at a seal you can grease.

A crack is not a seal you can grease

A split in the plastic is the end of that canister. Grease and another prime will not close it. In this set the crack reports are individual UK reviews, not a percentage. On the Fluval 307 they include a cracked top cover and a body that cracked and leaked after about five months, plus a later pump fault. On the Hidom EX-1200, reviews include a cracked body on arrival and an impeller failure at about seven months. If the wall is wet from a split, retire the unit.

What a single review does not prove

These notes are anecdotes inside much larger star lines, except where the sample is already tiny. The 307 has 4.5 from 2,623 ratings, and the crack comments are individual reviews inside that count. The Hidom review that alleges fish deaths on the first day is one UK review, not a measured failure rate. Get help when water has reached a socket and you cannot isolate the circuit safely, or when the cable or plug is damaged. If fish are dying and ammonia will not fall after feeding has stopped, ask someone who keeps fish for a living. If the body is cracked, the filter is finished.

Common questions

Why is my canister filter leaking from the top?
On a Fluval 07, Fluval’s FAQ treats a leak at the motor-head clamps as the canister O-ring. Clean it, seat it in the channel, moisten it, and lubricate it with Fluval silicone lubricant A325. Vaseline and vegetable oil are the products that FAQ tells you not to use. The cover has one orientation, and the clamps have to lock.
What should I do if water is near the socket?
If the plug and socket are still dry, disconnect at the plug and shut the valves. If either is wet, do not pull the plug by hand. Isolate the circuit at the fuse or breaker, then unplug. When you cannot isolate power safely, get help. A damaged cable or plug is the same stop.
Can I smear Vaseline on the Fluval O-ring?
Fluval’s 07 FAQ names silicone lubricant A325 for the canister O-ring, and it says not to use Vaseline or vegetable oil. Clean the ring, seat it fully in the channel, and lock the cover in its only orientation. That grease step is for a seal. It does not repair a cracked lid or a split canister wall. If the plastic itself is wet from a crack, the unit comes out of service.
How do I tell a bad seal from a cracked canister?
A bad seal shows at the head joint or a hose connector, and it can stop after the O-ring is cleaned, seated, and lubricated with A325, or after the hose seal is replaced. A crack is water leaving the body or a split cover, including reports of a 307 body that leaked after about five months and a Hidom that arrived cracked. Grease will not close a crack. Retire that housing.
When is this a shop or electrician job rather than a reseat?
Get help when water has reached a socket and you cannot isolate power safely, or when the cable or plug is damaged. A cracked body is a retired filter, and a new crack is a return, not a grease job. Fish dying while ammonia stays up, after you have stopped feeding, is the point to ask a shop. One Hidom review alleges fish deaths, and that single review is not a leak rate.

Related pages

Fluval 207 or 307

Canister filter

Best canister filter when the tank is 60–220 litres

Canister filter buying guide: match the stated litres

How to set up a canister filter without a dry start

Sources

Public UK sources and the amazon.co.uk listings compared on this page. Updated 22 October 2026.

  1. Fluval 07 series, UK (retrieved 22 October 2026)
  2. Fluval 07 manual (retrieved 22 October 2026)
  3. Oase FiltoSmart 60, en-GB (retrieved 22 October 2026)
  4. GOV.UK: Electrical Equipment (Safety) Regulations 2016 (retrieved 22 October 2026)
  5. legislation.gov.uk: SI 2016/1101 regulation 35 (retrieved 22 October 2026)
  6. OATA: how to test freshwater aquarium water (retrieved 22 October 2026)
  7. OATA water quality criteria, October 2022 (retrieved 22 October 2026)
  8. Maidenhead Aquatics: Fluval 07 (retrieved 22 October 2026)