Hello all, I'm new to this but would appreciate some help in identifying my cactus and what the problem seems to be with it. Recently I noticed that it was turning brown on one one the off shoots. I returned to the shop where I bought it from and they suggested I could have over watered it. Unfortunately they didn't know what type of cactus it was even though there was many still in the shop!!?! Anyway since burying my head in the sand so to speak the base has developed some kind of white fungus, I'm now scared it will die! can somebody please help with the identification and what I should do to fix this problem? Many thanks for your time, David.