Siporax is a media instead of LR for bacteria to colonize. It is suggested to use 1L for 25gal. I keep it in my return section with slow flow, no light. It needs to be kept clean of any detritus, so it doesn't become nitrate factory. I use filter socks on my returns, also being in last section of my sump , no dirt gets there. I keep it in a box made of eggcrate, i take it out once a while and rinse it with saltwater from WC. I only use minimal amount of rock in my tank as you see, also there was no LR at all, it is all ceramic rock. Never had any problems with ammonia, nitrites, nitrates. It works if done correctly. There are many successful reef tanks using this method, unfortunately mostly outside USA, for some reason people here want to compare them to bioballs that are nitrate factory and don't work in reef set up.
Here you can see my sump set up