Just speaking from my saltwater aquarium days but I think the biggest difference would be the volume of water passing over the lava rock and lighting conditions.
Typical biofilters for saltwater aquariums are normaly under the tank in a dark cabinet where lighting conditions are prime for bacterial growth. Theres also an exchange of gases thats available by placing bio media in a filter compartment or in a sump tank that probably isn't as effective as some rock laying in the bottom similar to gravel.
People doing saltwater aquariums are creative in their filter media to say the least, I would look up some of thier DIY stuff and see what they may be using for some ideas.. who can say what will and what won't work.
I am trying to raise GSH in an 80 gallon horse trough. I siphoned water into a 5 gallon pail full of bioballs and then use a powehead to pump the water back up into the trough. The water became considerably clearer when we added this over the typical over the back carbon filter.
