Sand offers more suface area than crushed coral for calcium, ph
buffering, and bacteria colonization than gravel. Bacteria are actually good, thay are what converts ammonia into nitrites and then nitrates.
sterilizers and refuges do completely opposite things, as refugiums allow extra life to grow and UV
sterilizers get rid of the life in the water flowing through it.
I personally use sand and would love to have a refuge to grow chaeto and ulva for herbivore food and nitrate uptake, but I can't have anything on the floor (small children) and I am having a little trouble selling the $200 CPR AquafugePS to my wife