I use Pumice as base for my soil mix. It breakes not up (like Spongelite), holds water and nutrients and makes it is easy to readjust the ph. There is no humus in my substrate which gives good growth in the beginning but degrades quickly and blocks the aeration later, making repotting necessary. I also avoid fines <1mm in my soil. If there is later to much salt from watering built up, I flush the whole thing from top with lots of water, readjust the ph and apply fertilizer as normal.
Thats not my idea, its from an old lady having some cacti (mostly Mammis) for 10+ years in the same pot.
Recently there was a link to a very interesting article of a Romanian Journal here in the forum (about the "Stone Eaters"). Worth to read.