Why from removing sand you want to add sand now? What's the rationale? How much sand do you currently have? Do you want to create DSB? DSB advisable to do at least 6". especially since you're using coarser sand. If you do lesser, DSB is not achieved, it will just be a nitrate factory. Just for aesthetic looks, just need 1-2" max.
you can adjust your shift your tunze and return higher or angle higher so tt no sandstorm created. I wouldn't recommend puka shells as they just collect algae.