IT is possible that you have a damaged cartridge in a cartridge filter or the sand filter is not set on filter when you vacuum or the laterals in the sand filter are worn and it is blowing sand back into the pool.
Yes, the 3.6L filter is a cartridge.Yes, the 3.6L filter is a cartridge.
It is a paper cartridge filter.It is a paper cartridge filter.
A cartridge filter is inside an assembly as an element is its own assembly.
Filter out debris from the fuel.
Replacement filter cartridges can vary in price depending on the filter that the cartridge is inserted to. In general, a replacement filter costs about 40 dollars.
Backwashing is done to clean the filter media in sand and DE systems. Cartridge filter systems don't have a "backwash" provision. You just remove the cartridges and wash off the dirt and debris with a hose.
If the pump is working, then you should have pressure. Low or no pressure usually means that the gauge itself needs to be replaced. High pressure usually means the filter is clogged with debris and needs to be backwashed (if Sand or DE) or the Cartridge cleaned.
One of two possible issues... Remove the exsisting filter, check that it's rubber sealing ring is still attached to the cartridge. Then use a flash light and a small pick, and check to confirm that a previous cartridge gasket is not become embedded in the machined seating ring of the mount. If so, remove the old gasket, and reseat filter. A second possibility is that the threaded cartridge mount is damaged, and is not alllowing the cartridge to seat fully against the machined ring.
Change your filter
Check to see if you have debris in your hair & lint pot. If not, then check to see if you have debris in your skimmer basket. If not, then you will either have an obstruction at the return line, too small of an eyeball in your return line or your filter sand needs changing. My guess is that if you have a problem with clarity of your pool water during a swim year that the sand needs changing. 5 years is the maximum for filter sand. If you have a cartridge filter, change the cartridge. If you have a D.E. filter, disassemble and clean the grids. re assemble and re-coat. Oh, by the way, if you leave the filter openings exposed over the winter, check for critter houses.
Cartridge is not installed correctly or you have a crack in the manifold allowing dirty water to pass by the filter.