Tonga Branch
Porous Rock
Tonga branch as far as I know is some of the densest LR available on the market. My one tank had a majority of Tonga branch. Everyone said the tank looks like it did not have 1 pound per gallon, but some of the larger pieces were around 40Lbs! A 40 pound Fiji LR would be 3-4X the size.
Most tanks do not need more surface area for the bacteria that convert NH3 or no2. They process it quite well, and you do not even need LR for this. Bio balls even work for that process. There is then just a build up of NO3 left. The only thing that can remove NO3 I know of from a reef aqaurium is anoxic zones in LR. However if the rock is too porous and there is too much water flow through the rock these zones cannot establish due to the higher oxygen levels.
Personally I have never found the porosity of LR to effect the biological filtration. However I could see porous rock acting as a much better mechanical filter.