live sand vs bio balls.

I don't really know. I have never used sand at all. But I would advise one thing you could do is pile live rock in your sump instead of the sand.

 

Your live rock is your "main" bio filter. If you were to remove the sand though, i would do small portions at a time. Every time you do a water change take a section out.

 

And bio balls have fallen from grace...they are no longer looked upon as a good denitrification medium. They are thought to catch enough detritus even when used properly (above the water with water flowing over them, not submerged) that they become a nitrate contributor themselves. You can probably avoid this by using them in conjunction to filter socks and changing the filter socks regularly.

You can always put some sand in your refugium area of your sump if you have one.

--AJ