chrisexv6 said:
Did you remove the o-ring you had added to the riser/multiport connection? Could that somehow be interfering with the direction of the water flow?
I wonder if maybe the riser is "weak" and might be collapsing in on itself once there is enough pressure from dirty sand? Or even more of a stretch....if one of the laterals is somehow flipping vertical and shooting water straight thru the sand back up to the multiport....that would act like a channel, but if the lateral flips back down when you turn the pump off you might not see it (like I said, stretching

)
Bama Rambler said:
Here's a wild idea. When the pressure rises the filter body expands vertically just a bit and causes the connection between the riser and the MP to open up a bit. It would happen slowly and you probably wouldn't notice it and if the riser is just long enough to engage the o-ring then I could see where this might happen.
I also remember many years ago we had an old outboard motor that would act up at times and after many trips to the mechanic I took the carbs apart and while cleaning the siphon tubes (think riser) with compressed air I found a hairline crack in both of them. You couldn't see it with the naked eye but replacing them solved our problem.
I'm just throwing out thoughts because it's such a special problem.
It's back to normal with the extra O-ring and tape removed. The riser goes about 2" into the multiport valve body when it's installed.
The laterals on this filter don't fold, so they are locked in a horizontal position. Water flows into the laterals from the sand, except during backwashing, so that's not likely a problem.
Absolutely zero sand going to the pool, and I removed each lateral from the riser and looked at the whole works pretty carefully.
I've seen similar things where a small crack caused untold problems. Like an aluminum carburetor body that had a seam near a mounting screw. Only it wasn't a seam, it was a crack, and when the bike got hot it leaked air :x
I have tried to imagine where a crack could be located to cause such an issue. Clearly, the multiport was my first guess, and the second possibility that came to mind was a crack in the riser above the sand, or even near the top. Since I'm not getting any sand in the stockings over the returns, I think that tells me that the mixing of water is happening above the sand bed. I believe I checked the riser very closely, running my thumbnail over it to see if I could feel a crack. My next idea is to pull the multiport and wrap the riser with Gorilla tape from the sand to the point where the multiport sits. I wouldn't expect a permanent fix, but it should let me vacuum long enough to see if there is a difference.
Before, it wasn't such a big deal because it was early, but now we have 90 degree weather in the forecast, and I'm going to be under pressure to have the pool ready

. My 3 year-old grandson was ready to swim in April, and if he can't swim on his birthday on the 31st like I promised him then, I'm going to be in deep trouble.
