Yay! Finally got my laptop back up & running (after 3 wks!) My plant that is like yours...I believe has A. tabuliforme as a parent. I've been scouring my Aeonium book for a match, but so far none...that is a "for sure" species. Here, showing many rosettes, the burned leaves & one hanging rosette I was cleaning off dead leaves from, broke away easily. Clcik for larger view:

Fungus gnats appear when you use a peat based soil that remains wet for too long. Looking at your pictures, this is where they came from. This will also cause your leaves to get mushy from over-watering. Your mix looks very wet and water retentive so I am guessing this is what is happening here. If you were to pull your plant out you will probably notice there are not a lot of roots and you possibly have some that are black (rotting). It looks like your plant is also etiolated due to lack of adequate lighting. They will stretch out and get leggy in search of sunlight. A combination of these things is what is causing your plant distress. -Erica

6" is quite large for such a small plant. You could plant couple together if that's all you have. Problem with over-potting is that the soil will take much longer to dry out. It may look dry on surface, but still be too wet inside around root ball. It would be better to go to just 4" if single. It would be better to add some inorganic materials to your cactus soil (many of us don't use it at all, but some ppl do). If you can get some perlite, pumice, scoria, grit, turface - any or few of these would be great addition to your soil. Soil (organic material) should be kept to max 1/3rd of the total volume, even less for best drainage.

So I got some cactus mix to replant it but unsure if the roots have rot or not? I'm not sure what makes them healthy or rotted. Another leaf has shriveled and was easily pulled off since yesterday. Would rot cause the leaves to shrivel? The top leaves are still healthy and growing but I'm concerned that with how fast they're dying the dead ones are quicker than the growing ones and it will all die. are its roots okay? edit: I take it back, while repotting it I lost 3 leaves, not just 1, and I can see another that's shriveled and still attached. I repotted it but if its roots are bad I'll go and redo it to get rid of bad roots. And what should be done for it after being repotted in terms of water and light? And will it be okay with the fact that as it's going to be next to my lizard tank to get the light from her tank, the light goes from dark to light very quick, unlike next to a window where it's gradual light changing all day? Her lights are on a timer so they go on and off at certain points of the day but once they're out it's totally dark. I don't want to shock the poor plant either