Rhizo, that's strange. House Plant mushrooms never grew in my succulent mediums, which are kept dry. The few times they appeared were in tropical plants where soil was kept on the moist side. Especially w/o much light. Here, outdoor mushrooms grow in shady spots that are usually moist.. eg, beside trees, or in spots in the grass where foliage from trees shadows the ground. Have you ever seen mushroom kits? The directions read to keep wet/damp in a dark spot. I don't know much about mushrooms, just what I've seen in pots/grounds kept wet/moist, and mostly shady. I once lived in an appartment. The bathroom floor wasn't level, so when a shower was taken, and water escaped through the shower curtain, it'd settle in a corner on the floor. To top that off the bottom of the toilet leaked. Every so often, mushrooms grew in that shady corner. lol. Gross looking things. The bathroom window was a Block Pane, facing north. I always thought the wetness and shade caused those mushrooms to survive the bathroom. Toni

Fungus generally need moist conditions to thrive as well as decomposing organic matter......not a common situation with most cactus plantings :-) And the vast majority of them tend to be beneficial or at least benign with regards to the soil and the plants growing in it. It may be that what you are seeing is just an accumulated residue from fertilizers (do you fertilize much?) or hard water build-up but could be some sort of fungal manifestation as well. Just scratching or disturbing the soil surface may disburse it but flushing the container with clean, filtered water and then allowing it to dry can help. Without some sort of evidence to confirm, I doubt you have too much to worry about.

what i would do to be on the safe side is change up your soil mix a little to something a little more coarse maybe, and if you repot it, dont put into a pot that is alot bigger then the one it is in now. At the nursery here, yellowing of leaves on our kalanchoes means too much water. That sucker will also bloom for ya if you put a dose of food into it every once in awhile, and let it dry out completely between waterings, we found that, that kind of stress helps it set flower clusters, oh and make sure it gets plenty of light. In phoenix ours went out of bloom, so we put it in a shade house with 70% shade cloth, watered when completely dry and fed em as well, a month and a half later they started to form clusters of buds. I would say when you re-plant that you dont disturb the roots too much, if you do, you will promote rot of the broken exposed roots (not saying you will for sure get that) but thats the major thing that kills succulents when repotting, so be gentle. Another thing, rocks at the bottom of a pot is probably not the best thing either. I would go to your local nursery and see if they sell a formulated cactus mix, this should allow quick drainage, and the soil shouldn't stay too wet between waterings, it will also cancel the need to put rock on the bottom of pots which just hinders drainage. Google around for different soil recipes.. i mentioned in another post here that with my succulents, i use pumice, coir, and sand (not play sand). I hope that babbling helped somewhat :\

I googled dog vomit fungus - tons of info, one source linked below. Nasty looking, huh? Here is a link that might be useful: dog vomit fungus (slime)