Adding infill sand helps to weigh down the turf, adds stability, helps prevent turf fibers from flattening or crushing and adds ballast. NEXT, add Infill Sand (Silica 16/30, 20/40 or Envirofill 16/30 size) SLOWLY by hand. Add 3-4 lbs per square foot (if your total project size is 500/SF then you will need about 350 lbs. of infill sand) of turf depending on your turf height & density. Add sand  by broadcasting along the grid lines in either direction, then using a "Deck Scrub Brush" brush sand against the fiber direction until it stands up evenly and sand is dispersed and not clumped. Be careful not to be too heavy handed (too much / too fast) and bury any fibers which will create an uneven surface. You should be adding enough sand to just below the paver surface throughout.  Repeat this step until desired finish & firmness is achieved. Tip: Use a shop vac to clean up the excess sand on the tiles and re-use.