Lately I've been asked many times about using pasir malang or Lava rock as substrate. I've heard of this 20 years ago and I've tried that too as you can see from my old picture. been there done that Firstly lemme explain what is Pasir malang, they are Lava Rock or Volcanic rock. Very porous in nature, an excellent filter media. Couple with an ion negative charged acts like a magnet to contaminations such as heavy metal and so on. Now lets get back to the question, is lava rock a good choice as a substrate? Is it also advisable to use sera siporax as substrate? this will saved us plenty on canister filtration set up. Right? wrong! why do canister, trickle or any sort of filtration designed in such a way that plenty of oxygen supply are pumped onto the media? Because beneficial bacteria needs a lot of oxygen to operate or they will die if inadequate O2 is available. What happen to places with low oxygen supply? these are the black site or black area that spawn bad bacteria