I've seen home depot lava rock recommended many times and I suspect it's fine if it fits in your filter and you check your water paramters to make sure nothing leeches into your tank.
The use of "sponge" biomedia gives far less surface area per cubic inch than ceramic and other conventional bio-media ..... but the advantage of it is that it can be rinsed out in aquarium water whereas ceramic and other commercial biomedia cannot. I suggest people listen to King of youtube DIY aquarium Joey Mullen is usually spot on. Go here:
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As far as needing to replace biomedia, I found he is correct (whether it's lava rock or Fluval C-Nodes or high end Fluval Ceramic), that bio-media is going to get "sludged up" and needs to be replaced.
As an aside, I pretty much accepted the notion that biomedia never needs to be replaced. However, I noticed the pad over the drip tray of my oldest Fluval C3 HOB was totally clogged causing the water to completely bypass the bio-media and fall onto the "lip"/outake of the filter. When I scrubbed hard and rinsed it in distilled water I was uderly amazaed at how much "gunk" came out.
Then I looked at the 6 month old C-Nodes and Seachem Matrix sitting in the drip tray. It is by no means clogged but there is a significant "growth" of slime and gunk that will in fact render the biomedia to become less effective over time. Manufacturer says rinse/replace half every six months. I figure once a year is enough.
This really shocked me since my water is crystal clear and passes through 100 micron polishing pads before being passed through the chemical filtration chamber and biomedia tray.
