Unlike other “bag” solid covers, Merlin’s “tension-Secure” solid cover combines safety with the complete barrier a vinyl cover provides. The water-resistant solid cover keeps out dirt, dust, and sunlight, which means no algae growth. It also means you open your pool to clean, crystal clear water. The Solid Safety cover uses either an automatic pump or micro-filter panel to remove any standing water. The Window Mesh Drain Panel uses dual layers of micro-mesh material to let water (filtered to 250 microns) pass through.