I have a 150 sq ft cartridge filter that appears to be allowing dirty pool water to by-pass the filter cartridge. It appears to be getting past either above or below (or both) the blue gaskets(?) on the ends of filter cartridge. I see sediment, cloudiness and small leaf debris (ie: pretty much anything that can get past the leaf catcher) coming out the outlet back in to the pool, especially when vacuuming. After much tearing out of hair, I eventually noted a poor fit where part of the filter housing cover fits into the inside of the cartridge. I have been able to reduce the amount of by-pass significantly by adding electrical tape to the filter cover to produce a more snug fit (see yellow tape in the second photo), but I have not been able to eliminate the problem fully. I suspect there is something mechanical going on that I'm missing, as the problem only started happening a few months ago. I've bought a new cartridge, but this has not helped (in fact it made things worse probably as it's a slightly looser fit). I've also confirmed that the spring holding the by-pass valve (refer bright blue component in third photo) is sound - I can't move it at all.

The pool is an old concrete (painted plaster?) 55k litre (14k gallon) inground one. The pump is a 900W Tempercon swimming pool pump and the filter is a Filtermaster FM150 150 sq ft cartridge filter. There isn't much info about this filter on the web, but it looks very similar structurally to a Davey EC1500. There is a pipe right up the middle of the cartridge which has some black fittings on it. The filter sits on the mount shown near the bottom of the pipe in the photo. The small black ring (shown near but not at the top of the pipe) is broken, and no longer stays put. The bottom ring has become unglued. The result is that the pipe may be sitting lower than it should (it drops to the bottom of the filter). It looks to me like the pipe may be designed to sit off the bottom of the housing (supported by the mount which is in turn held in place by one or both the black rings), but I'm really not sure. If I sit the pipe high enough (using tape keep the pipe from sliding down below the black mount) - it (and the black "cap" shown on the top) does fit a ways up into the dome of the housing cover (ie: inside the bit wrapped in electrical tape).

I have noticed that the cartridge doesn't sit perfectly upright in the housing, and when the top is put on I'm guessing it may be lifted slightly on one side at the bottom. There doesn't seem to be much compression holding the cartridge "down". I did see the thread Intex cartridge filter passing sediment back into pool... which kind of reinforced this thought.

Appreciate any thoughts anyone may have around how to set-up the white pipe properly, what it's purpose is, and if possible how to stop the by-pass. It's driving me crazy...

Many thanks