Quote Originally Posted by Oliver

At some point the small ball size in a grow bed becomes problematic and difficult to keep out of the siphon and plumbing. Increasing the size of the balls reduces the surface area proportionally. In the case of gravel, it is usually larger in diameter than expanded clay and gives less surface area for the autotrophic bacteria to reside. As a result, you will need more volume of media to give the same bio-filtration as the smaller diameter balls.
Very true! I used pea gravel mixed with river stone because I wanted the denser surface area the pea gravel provided. If I had it to do over, I would have gone 100% river stone! Despite a proportionate fish weight to filter ratio, mechanical filtration and settlement tanks, I have had to clean out tilapia turds clogging my growbeds twice in the past few years. That is one NASTY job1 The larger diameter river rock is much less prone to clogging and easier to clean if it ever does.