How to Stop a Canister Filter From Leaking
FOAM CART 2010

Retail Price: $19.99
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A few weeks ago I bought a used 130 gallon aquarium with a Eheim Pro II External Canister Filter. I decided to open the canister to clean the filter and see if all looked okay. I undid the clamps, got all the media out and put fresh filter media back in and attached to hoses.
Wauw, it started leaking like crazy. The problem is really bad when I switch the filter off, and less (but still leaking) when I switch it back on.
Where did I go wrong?
Answer
It sounds like a problem with an old o-ring the needs replacement. You will need to replace it, but when the damage isn't to bad , you may be able to make a temporary fix, by putting some silicone lube on the leaking seal. This is a temporary solution because you don't want to have a damaged o-ring in your filter and run the risk of pumping 130 gallons of water on your carpet.
If the o-rings are really old, I wouldn’t try to remove them until I had replacements in hand.
Tags: fish tank filters leaking, aquarium filter leaking, canister filter is leaking