I first started noticing there were strange pale looking spores in the pot of one of my cacti. I repotted it and removed as many of the spores as possible (they were underneath the soil), but after coming back from a weekend away, the soil in this cactus is still moist, meaning I don't think the roots are absorbing any water. I water all my plants at the same time, once or twice a week, and only water them once the soil is virtually dry. They're in proper cactus soil with good drainage on a windowsill with a lot of light during the day, staying warm all the time. I removed the plant from its pot and dug around until it came out. I think the roots still seem to be intact, but I don't understand what these spores are. I've attached pictures, and for the moment I have removed it from the soil, but I can't work out what is the problem and if it's salvageable. Any help would be much appreciated. Charlotte
Potted Cacti Issues
Certified GKH Gardening Expert
Though it is a cactus mix your using and you mention that the soil is moist, you likely have watered to heavily and this is the cause of fungus in the soil.
You may want to amend the mix with some sand and peat. This will allow the soil to dry out more quickly. If the soil remains soggy is only a matter of time before the cactus itself begins to suffer from root rot.
You can treat the roots with Neem Oil. This should help with the fungus.
Here are a couple of links for you.