What sort of tank do you have? How big? How much sand do you want to add? Is there sand in it now, and if so how deep?
If no sand now, then I would add it all at once. It will make a big cloudy tank but it will only be once and then done. I think that is less stressful to anything in the tank. I have added sand to many tanks over the years and always just went for it.
If you have sand in there now then it may be a little different story, you don't want to kill what's in there so don't cover the old sand with more than a quarter inch or so.
I have added sand to tanks loaded with coral and never had one problem. Reefs have murky stormy days too! haha.
I never rinse the sand but I know you can cut down on the dust if you do. I put the sand in a ziploc bag drop the bag to the bottom of the tank and slowly empty it.
I have also got a piece of PVC and poured the sand down the PVC pipe to the bottom to get it in to hard to reach areas as well but this can be a pretty messy task lol (sand all over the floor unless you have a great helper).
