[greenbean36191]

Bioballs are a great surface for the bacteria that convert ammonia and nitrite into nitrate. However, the bacteria that convert nitrate to nitrogen do most of their work in areas with very little or no oxygen. Bioballs don't provide a suitable habitat for them, but because LR has internal surface area too it does give them a place to live with low oxygen.

Basically the bacteria on the surface of LR can break ammonia down to nitrite and then nitrate and then the bacteria inside the rock can take it all the way to nitrogen. With bioballs the bacteria only live on the surface and can only break it down to nitrate and then it goes back into the water to be processed somewhere else.

Edit: Man I'm slow.