Question
white, fungus like growth, covers much of the cactus. what should I do?

Answer

scale on a cactus It's hard to say what you have with out a picture, but here are a few possibilities:  The most common pests that affect succulents (kalanchole isn't a cactus) are mealy bugs, root mealy bugs, aphids and scale.  I have a picture of the last and will include it.  These insects secrete a substance called honeydew which allows fungal spores to attach.  If the plant is covered with a fungal growth it is very hard to treat and you are likely to need a new plant.  If you want to try to treat, scrape, or with a large infestation, try to hose the damage off, unpot and wash the roots, cutting off an y dead ones, pot in new well draining soil with a bit of insecticide/ fungicide and watch for any signs of new infestation.  Be sure to isolate you plant as well.  Then spray with an insecticide/fungicide at the first sign of any disease as needed.

Succulents attract insects/fungi when they are over watered, don't have enough sun or are in a soil that doesn't drain rapidly.  In the case of your plant the leaves have a nice powdery finish called a "bloom". No possibility this this is your problem?

Hope this helps.  If you could send me a picture that would be great.

Maureen