Recommended hours of filtration = 9 or more.
I’ve saved the best till last. DE (as it’s commonly known) filters can filter particles as fine as .1 micron. This is ten times better than a cartridge filter and 40 times better than sand. Wineries use DE filtration to remove particles from wine. Diatomaceous earth is a fine white powder, which is made up of the exoskeletons of marine plankton. Most of the Diatomaceous earth used in this country comes from ancient sea beds around what is now Los Angeles California.
A diatomaceous earth filter has several PVC plastic grids inside which are covered with Polypropylene mesh.
The mesh is fine enough to hold back the diatomaceous earth, and the earth allows the water to pass through while stopping the dirt. Particles that are smaller than 1-micron pass through and remain in the pool water. Some problems with DE filters include, if one of the grids inside the filter develop a rip or tear then the water passes right through. This is easy to diagnose since the DE powder also passes through and makes a grayish powdery mess on the bottom of the pool. Your pool sweep stirs it up during the day and makes the water look cloudy. If you turn your pump off it will settle back down to the bottom. You’ll need to replace the grid. Over time the mesh becomes brittle and it’s very easy to put a finger through and cause a tear.
Also if a grid isn’t seated properly where it plugs into the base of the filter housing you could have a leak allowing unfiltered water to pass through.
The polypropylene mesh that covers the grids is so fine that it can screen out the calcium that’s in the water. When you take the filter apart and look at the grids look for grayish white patches that indicate calcium. If significant portion of the grids is covered with calcium, you need to take the grids to your favorite pool store for an acid bath. This will remove the calcium and allow the water to flow more freely through your filter. It’s recommended that you acid wash your filter grids annually.