regarding biofiltration, your current sand loading counts as a helpful factor in your tank. the tank has highish fish bioloading, so the sand currently in there is pulling some weight so to speak...removing it and switching out with highly rinsed, no silting black sand you show only has the risk of removing out a vital link in your active surface area but there are still some hedges and ways to predict before you do all this work.
I myself switched out an entire sandbed for one that wasn't live...harmless in my tank, because of no fish and high live rock to water ratio. my live rock does enough, so the sand was incidental to me.
In your tank, a specific test can tell you if yours w be ok. You have to part out the whole reef in buckets, strip this old sand out, put all the rocks and fish back in, and use a non api ammonia test of high quality since everything is on the line here, to see if your rocks alone will support the fish bioload, I give you 99% chance they will. 99x9%, live rock is that good. If after a week in the no substrate tank your whole system shows zero ammonia, spend well on the test kit here, then you are proven safe in your sand switch.
but no guess is ever required when recycling is at hand, specifics exist. if your tank w digest the waste on live rocks alone, then adding a bunch of rinsed out new sand is harmless. if you carry true low level ammonia not from an api test kit, your sand is needed or this needs to be pre aged before use. specifics!
B
