I've, only, some experience with treating fungus with sulfur on roses, but, I do use this to prevent rot on succulent, orchid and cactus wounds and cuttings. It's helped stop rust from developing on the rose leafs. Perhaps a light dusting of garden sulfur could stop it's spread.
I'd think any bleach would be more harm than good. That can be very caustic to the surface of any plant.

This is not rot. It is more like mildew.I have already used sulfur, cinnamon, Daconil, Bayer 3in one stuff. I am thinking I will try a gentle scrubbing (maybe scrub is wrong word) with soap and water. And work up testing on a samall surface first. and rinsing off immediately. I might have Killed the growth of the dark already but I need to be rid of it on the surface. I am hoping it has not "bonded" with the leaf surface.

Experiment with an area of the effected plant rub a Q tip with a small amount of tinactin or some over the counter foot fungus cream.

Cant confirm if treating an entire gasteria this way would solve the problem as but did a good job for me with a noticable spot treatment.

Other method that would also help is to change the fungus growing enviroment. Would think better air circulation would be the best part of the fungus growing enviorment to change.

I see you have some nice babies, so you've obviously had the plant for a while and care for it well. So I don't want to question your mold diagnosis by any means.

I have a similar looking place on my G. 'Green Ice' and thought it was part of the process of losing the outer leaf. The spot does not rub off and it does hang around for a long time without spreading on the plant. I've had it before and when I removed the leaf, the problem was gone. Was I wrong and I haven't address the real problem? I have used copper fungicide on my succulents with success, but it sounds like you have tried that. My soil is about 6 months old.

I have this showing on my plant right now. Since everything in SWFL molds, rusts or rots, I may have overlooked the obvious.

NN, Not lack of ventilation. It is on a raised (11ft off the ground)covered porch, open on three sides facing south wind. Today, 25MPH winds. LOL. Bird feeder is clanging away. Blown dust, silt, etc. that then got moist might have created the situation. Tinactin EH. That is an interesting option. I do have some.I was thinking about changing dirt and going with mostly pumice this time. I think the dirt is 4 yrs old. It is a combination dish garden

Crenda, your spots do look like they have eaten into the surface. Mine are on top.

I did get my coffee and soap and water and peroxides and I washed the plant and with gentle rubbing , most came off. I think I might tinactin the crevices. NN, did you then wash it off after awhile?

Here is the whole pot in younger cleaner days.
{{gwi:556440}}