I have had a problem in the past where the impeller cover retaining clip breaks during maintenance and goes unnoticed causing that issue jeaninel, but not just randomly coming loose. If I was in your shoes I would try swapping the cover, since you have two, and if the issue persisted and would then purchase a replacement.
fluval 405
- Thread starter 1972ford
- Start date
Good idea. I'll try swapping them. I've been meaning to call fluval about it too. Just haven't had time.
I'm not a fan of the smaller fluval units. Fx5 has generally good reviews here, but I would never buy a new 406.
I have slowly made the switch to bigger tanks and sumps. Filter socks are sooooo much easier! 
I don't think they are awful, they just didn't feel cost efficient for me. I find other options more effective and I felt like the maintenance was difficult. If you don't want to part with them I would fill it with bio and put a prefilter over the intake. An ac70 will blow it out of the water for mech, and if used together will leave you a very reasonable set up.
I wouldn't be as bothered if it wasn't such a pain to take apart while maintaining an airless prime. The hardware is good, the design is lacking imo.
The one I used in the video is a 406 that if you noticed has no power cord. The seal gave on the motor and almost set my fish room on fire. I have since resealed it and it is now filled with bio and daisy chained to an older 405 that still works. 
i got an old 404 when i bought a coupe tanks and the top is a pain in the ass to get off. that, and the fact that the seals give out are the only things stopping me from using it. oh! and priming it. PITA
All of the factors above contributed to me chucking the 406, I just run internals and sponges now; not a huge bioload anyway.
