Blow-By in DE Filter

I have a 25,000 gallon in ground pool and an American Products Titan CM 48 square-foot DE filter. A few years ago I replaced the spider gasket in my multiport valve.

Lately, I've noticed that 1-3% of the debris that I vacuum up gets blown back into the pool.

Where are the likeliest sources of the blow-by? Rip(s) in the filter grids (all but one is more than 10 years old)? There's a crack in the top (manifold) of the filter grid assembly but it's hairline and I have doubts about whether that could be the source. I haven't taken apart the multiport valve to check directly on the spider gasket.

Thoughts and information about previous experience appreciated.

Sounds like it may be time for a new and BIGGER filter or
an impeller on your pump that has a slightly lower flow rate.

Sounds like your filter is succumbing to the too-big pump syndrome.

Or it could just have some worn-out replaceable parts.

Carl, what makes you think that the pump is oversized relative to the filter?

I have replaced the pump motor (1 1/2 hp before and after) and I once had to glue the impeller back together.

I've owned the pool since 1999, so the equipment is more than 10 years old (I don't know when it was built). What's the expected lifetime of the various components?

Operative word is MAY be oversized--you are getting blowback. That means something's broken, something's too low, or something's dealing with too much flow.

Life expectancy is of course determined by how much stress an object is under.

I disassembled the multi-port valve yesterday and discovered that one of the "legs" of the spider gasket had come loose. I dried it out using a hairdryer on low, and crazy-glued the leg back in place (only getting my fingers stuck a little).

The jury's out as to whether this will solve the blow-by problem, but I'm optimistic as the leg in question was between the outlet of the pump and the return line.