its not that hard, the basic summary is that the bacteria aren't a concern, you can't remove too little or too much sand and cause a bac insufficiency. Bacteria don't factor in a sandbed clean, keeping detritus away from sensitive animals takes priority so that thread is a bunch of tanks doing an ordered, stepped disassembly, we do whatever we want to the sand at the intercept point (rinse or replace it) and then we set back up in ordered steps and we never lose one single organism other than some sandbed worms that don't do anything but make whole waste pellets in the sand, like earthworms.