Review on Fluval Motor Seal Ring Gasket by Erika Martin

I started with Stone Age aquariums (aquariums with metal frames and filters under gravel). When I moved into my first Fluval 301 I was impressed, but it had a few flaws. Maintenance was problematic, the impellers stuck together, the impeller cover broke easily, the impeller shaft was difficult to clean and replace, and they often cavitated easily. They had to buy extra shut-off valves on the line or use buckets. Priming the pump often required priming through the mouth (dirt). Removing the air from the impeller was an art. The new Series 5, 6 and 7 address many of these earlier problems but introduce a major new problem. O-rings worked well in round cases and rarely failed. Now with a round o-ring and a square body we have a problem with the seal design. They really should pack each filter with a few spare o-rings, and I suspect they shouldn't because the head gasket design is so imperfect that it often still leaks. I have used silicone grease, 303 and even KY jelly to lubricate and seat seals with mixed results even on low mileage filters. I found the best solution is to have a VERY clean groove and o-ring. You can treat it if you want, but silicone grease won't do much good. The problem is that the o-ring deforms at the corners of the square body and never returns to its original shape. New O-rings are expensive and often leak. I've found that placing a precision bead (half the width of the o-ring) of good quality clear silicone around the bottom edge of the o-ring is a game changer. It should be sparse, neat and even around the o-ring, the smaller the better. For application I use aq tip. Do not place anything other than the bottom of the o-ring and allow 15 minutes to set before reassembling. Then give it 3 hours before refilling the filter with water. I place it in a square cake pan to test for leaks with standing water. Then I wait a few hours and apply pressure to the cake tin before I feel secure. Silicone cures with moisture, so as long as it hasn't leaked within the first 24 hours you're fine.