To me it just looks like a mild sunburn. When did you get them? Did you put them straight into the sunlight (direct one) right after you got them?

If it indeed is a mild sunburn, then the plants will outgrow it, but you need to acclimate them slowly to their new environment and higher amount of sunshine. Otherwise they can develop ugly, brown scars.

Also the pot looks pretty overpopulated and it does not look like its got any drainage holes on the bottom. If thats the case then the water will take a lot longer to evaporate and you are putting your plants into a higher risk of root rot. My humble advice would be to grow every plant in its own pot, with drainage hole(s). Even on the picture the water is sitting in the pot, if the plants will sit in water for more than few hours or a couple of days, the rot is inevitable.

I did put them directly in my window and Denmark has had an surprisingly hot week so I'll definitely remove them from the direct sun and see if it helps.

I did actually consider if it were overpopulated but I followed a plant book and therefore thought it didn't hurt the plants?

The visible water is isolated from the soil I tried to create a sort of pond looking feature.

Agree with the above. Was just going to comment on pic four, that reflection says its waterlogged to the extreme! Best in separate pots and with at least one hole and in a better gritty mix, tons of info in the search box for a better gritty planting media. If you want community pot, place individual pots into large container, fill gaps with rocks. Some white looks like excess salts as shown on the Gollum crassula in pic 5, it's natural. Others not so sure about, others may come in and help. They need more space, more air movement around them, they're too crowded and creating their own microclimate, succs need drier conditions. The soil is first thing that needs amending.

Gill

Oh and I've only had them for about 2 weeks

Even if the water is isolated, I would still remove it. It is going to keep evaporating, creating more humid environment, which succulents hate, and creates higher risk of fungus infection.

The plants should be separated into their own pots. If you keep them all in that pot, later as their roots will grow, they will get tangled around other plants roots, possibly strangle each other and create more infection-prone environment at the same time. And then it will be significantly harder to separate those plants, without heavily damaging their root system.

Another problem that I see with keeping them all in that one pot is that you got heavy-direct sun liking plant there, Echeveria, combined with only indirect (or small amount of direct) sun liking plants, such as Haworthia.

I prefer to use clay pots, but whichever you decide to use, it must have drainage hole. For soil, all the plants that you have there will do well in a mixture of silica sand (not fine sand), perlite and some peat moss. Make sure that the peat does not make up more than 50% of your soil mix, like many store-bought "cactus/succulent soils" contain.

IMO, you have few issues:

some sunburn possibly

excess salts - on Gollum, as Gill pointed out

I am suspecting some mildew - the jade leaves and stems are showing signs of it (can't tell if it is on other plants). The air flow around the plants is also important. If humid and stagnant, use small fan to improve. Potting them into individual pots will help some.

Drainage is most important for succulents, as in mix and container that needs drainage holes. I would use much less than 50% of peat in the potting mix - it is either water retaining (staying too wet for too long), or if dry, becomes hydrophobic. If you could get some grit (often easier to find than silica sand) and perlite (pumice, if you can get some easily) make a mix of equal parts of these 2 and small amount of soil - for example: 40%grit + 40%perlite or pumice + 20%soil.

I would get rid of that 'pond' - while nice, it creates extra moisture for succulents.

Okay thanks, I will try and follow all of your suggestions. It just annoys me because I follow a instruction from a indoor gardening book that had a bowl of succulents with a pond and it looked so cute.

What do I do about the 'mildew' I haven't heard of that before?

I'm intrigued by that book with the succs and pond illustration.....any chance of a pic of that pic? So there is actually a reservoir of some kind within your planter to hold the water?......that's crazy, for succs anyway! There are plants that would benefit, but definitely not these.

Gill

I agree with Crenda, I think there is so much "not so good" information out there on succulents.

Just the other day I watched a string of videos from one lady who basically gave the same information that Emma got from this book. She said use any cactus soil, no perlite or grit needed. Use any container no holes needed, and that there's no such thing as over crowding succulents. Something told me what she was saying just wasn't right... That not all succulents were the same..

That's when I continued my search and found this forum...

Not all of her information was bad, and the only reason I know this is from this forum. I've learned more in just a few days of reading the back posts then I have in a year of google searches.