During the Backwash Cycle, water flows up at a fast rate to flush iron, minerals, dirt and sediments from the resin bed. The resin bed expands and lifts for cleaning.

This is one advantage of the Water-Mark Softener vertical type unit over the tube type that lays flat on the ground or dock.
Those types of units load up on sediments faster. Why?

The resin inside the tube type units must be packed in tight, so the water will flow thru the resin. They have to do this so the water will not by-pass the resin. If the resin is packed tight inside the unit, it can’t expand and lift to flush out all the sediment during backwash. So, over time, the unit may see increased backpressure and not flow that well. That’s why all water softeners installed in homes are vertical, like the Water-Mark Softener. Also, never replace the per-filter canister with a clear unit, like some other brands use. It’s important to keep sunlight from your water supply, or algae and mold will grow, especially in stagnant water.