The reflection is just a shiny finish inside the saucer. They are in basic cactus/succulent mix. I watered them about a month ago. I did buy another cactus recently that died from rot about 10 days after I brought it home. I think it was sick when I got it. Now I’m worried that it made these guys sick too.

Maybe I should just start over? I don’t want it to spread to my other cactus/ succulents

If it is rotting it will feel soft - the ONLY cure is to cut away all the rot back to sound, firm flesh. Sometimes the rot is all the way up the vascular cambium and the plant is a goner. But if you can cut all the rot away, dust the cut surface with cinnamon powder and hope for the best. Good luck with it.

The thing is..How can you prevent it from starting in the first place?

If you would like ideas, let us know what you think might of caused it and what kind of environment it's in and what kind of mix you use. Too, if you could tell us if you use fans and or water from above and if they are grown in cold windows.

Gill, knows where I am coming from...

Rot can often start in the roots and travel all the way to the top of the plant up the vascular cambium. Don´t let the roots stay wet too long. The fungal spores that cause rot can get in through any nicks in the skin or other accidental minor damage. And often there is no obvious cause. I often lose a plant in winter to rot - although all the others in its cold frame are totally fine, in the same type of mix and in identical conditions. But the biggest cause is overwatering - far more cacti are killed by too much water than by keeping them dry.

When people say they constantly have problems with indoor cacti and succulents dying, that can be a clue that there's a mismatch between the plants they're buying and the environment in which they're growing them.

Cacti in particular need a lot of light to stay healthy. This is difficult indoors at any time, but even more so in the winter. I suspect you're also overwatering them, which is easy to do to any indoor plant in the winter. I see you've top-dressed the soil with gravel - that's just going to keep moisture in the soil, which not something you want to be doing with an indoor cactus.

There are probably good solutions for growing cacti indoors but they probably involve a lot of experimentation and, I would guess, an investment in grow lights. If you don't want to go that route I'd limit your indoor plants to tropical houseplants or shade-friendly succulents that are proven to do well indoors in low-light situations.

Ok, so we live in a new manufactured home so the humidity is probably higher than they would like. Also, the air temperature is 62 degreesF at night and 75 degrees F during the day.
I water from the top, but sparingly....like I try not to water so much that it puddles in the tray.
I do have a fan that circulates air into the kitchen from the living room. It’s not blowing air onto them but it is pulling air from their area.
They are on a shelf a few feet from a window, but not in the window.
I have a much older cactus (22 yrs) across the room that I adore that I am worried might get sick.
I’m willing to cut off the rot and hopefully they’ll recover. What do you think about removing the orange part completely? Do you think that might give the lower green guy a better chance? Or no?