bio filtration

Hi everyone, I'm starting up a seawater moving bed biofilter and purchased some new plastic bio-elements. Although the density of the media is ideal, they do not integrate into the water column and stay on the surface, even with harsh aeration. I would like to ask if you have any suggestion on...

I know this could possibly start a big debate but that is what i need. In your opinion, what is the best non-commercial biological filter media? ie. lava rock pot scrubbers? I need a ton of it like enough to fill a 50 gallon drum worth. what is the best and dont cost an arm and a leg?