Dirty water returning to pool while vacuuming (on Filter setting)

[gdesone]

In ground pool with 11 year old filter and sand. Last summer I noticed this problem while vacuuming after shocking pool for visible algae.

This spring I am late on opening pool and it is very green. I normally super shock it and vacuum up the grey algae lining the pool bottom the day after before adjusting PH, etc. Upon vaccuming on Filter setting we can see the return jets streaming the brown-green water back into the pool making the water all dark and cloudy so hard to continue vacuuming and pointless it seems..

I guess I could vacuum on Waste setting but this will empty the water level pretty fast only having a 1 speed pump.

Is the problem the 11 year old sand (channelling?) or the multi-port valve ? Is there a test to determine which is the problem ?

[Teapot1]

I would agree, channeling is quite likely. If you are going to swap out the sand, consider Dr Drydens AFM ng glass media, it doesnt channel because the surface cannot be colonised by bacteria (self sterilising), its easier to backwash and filters as well as DE without all the mess and expense. Lasts the life of your pool.