Levels are not good. Take your C&S mix and mix it with 50% perlite - that will get your mix right.

Meanwhile, depot all of your plants, get rid of the pebbles (save them for later, you can use them as top dressing), and put pieces of screen appropriately cut over the holes.

Repot the plants using your improved soil at the level they're at now. Wait two days, then water well. Give them as much light as you can. At this time of year, watering every 10 days is OK, but if you can, grow them outside when it's warmer (consistently above 15C / 60F). Acclimate them over a period of weeks to full sun.

It's likely they didn't like the way they were potted, but should recover soon. Many of those plants do grow from the top, dropping lower leaves, but I suspect in this instance that they were showing their displeasure with their condition below the soil.

Your Haworthia - the red plant - did you purchase it like that? It looks as if it's painted, but they can also colour up nicely, depending on the season.

ETA - as long as you're in there, I'd add at least three more holes, or enlarge those that are already there.

Rocks at the bottom do not help drainage - having extra holes (as you drilled) is much better.

As cactusmcharris suggested, make a mix adding lots of sifted perlite. Use kitchen sieve/strainer to get rid of dust, or at least rinse perllte using sieve. Screen over the holes helps a lot - use window mosquito screen, or drywall mesh tape. You could buy small pieces of plastic embroidery 'cloth' in hobby shops but it may have bigger holes - I am not sure since I never used it. You could use piece of landscape cloth over the holes if in a pinch, or even paper coffee filter.

All plants need more light, except haworthia (red painted one). Sure you could give it same light as others, but if the lighted space is limited, put that one where it is less.

How far are the lights from top of plants? Maybe too far, if so - lower it. BUT do this gradually in order not to burn them. You could get a timer to set them go on automatically, and depending if there is any natural light (and how much), they can be set up on 12hrs cycle.

Watering 1/mo could be too little - BUT it depends on your mix and overall temps. I am saying it because planter is so shallow, and could be draining fast. Just make sure you don't over-water - check mix deep into planter using a wooden/bamboo skewer or chopstick (in a pinch, pencil will do :) Succulents will recover from under-watering easier than fro over-watering. So keeping them drier is better than wet.

Thank you so much! I'll fix the potting soil and see if that does the trick. I'm hoping they bounce back since I do really enjoy having them on my desk.

The Hawthoria was purchased like that, I tried to clean the paint off once I realized it's not naturally red, but the paint wouldn't budge. It's sort of spreading, so the inside where the arms weren't covered are able to get light and breathe.

s,

Rina gives some excellent further information.

Good. Yes, they do grow out of their painting, eventually, but until then, it ain't natural. It's a bit of a marketing scam. Did they say on the plant label anything about it?

They're still in their growth phase, so about the second watering I'd add some 1/4-strength general fertilizer to your water.

They didn't say that it was painted, I didn't realize until I had already planted him (the plant) in my little pot. I like his pop of color, but I am disappointed that he's probably not doing great since he's covered in paint...

The label didn't say what any of them are.

We can ID them - is it possible for you to shoot individual pics of all of the plants and show them to us?

That light is pretty much garbage. I believe this style is a lot better but still garbage. As far as your succs go, they probably don't need any watering because they don't have any light that can sustain them. they are most likely dropping leaves from not enough light.