Yes. I have heard that scrubbies, bioballs and a whole bunch of other things make good bio filter media but I also read that volcanic rock is pretty good and I can get a whole pick up load for a few dollars and gas. What's wrong with using volcanic rock as bio-filter media?
Here is another... Filter Material: Cover the entire area with bio-balls, lava rock, scrubber pads or any other material for the bacteria to colonize. Source: http://www.pelomedusa.com/Filter.html
I've looked at the biological filtration filters and I don't understand what the difference is if it is above ground or under ground. Isn't what I'm doing the same thing? Why wouldn't the lava rock develop micro organisms that filter it under the gravel just the same as if I were pouring it through the bio filter on top? I always had a clean fish tank when I had an undergravel filter in my aquariums and I never had to change the water. I realize it will take a month or two for microbes to build up in the gravel but how does it differ from using the bottom of the pond as one giant bio filter than running everything through a box on top the pond? It seems like both would work equally well; unless one were a lot bigger.
