Very nice group of succulents Alain. I think I like the last one best. Is this Cotyledon orbiculara? It's very clean and nicely plump. Beautiful colors. I also like the Parodia scopa. The spines are very uniform and clean. I have trouble with these very white spine cacti because of all the calcium and magnesium in my well water. It mars the color of the spines and it very hard to remove. What's your favorite?
I like the last one although I do not know the name but I have sentimental reasons for liking the Haworthia, The water here is hard but so far so good. Do you have an alternative source of water?
I am on well water and the pH varies considerably depending on the time and year. I recently check the pH of the water and it was 7.8 to 8.1. Quite alkaline (hard). I do collect rain water but not enough to handle all my plants. Recently I have been acidifying my water with vinegar to try and get the pH down to about 6.0. I haven't been doing this long enough to determine whether it is having a positive effect on the plants. I am going to begin checking the pH of the leachate from my plants on a random basis to check the pH of the media.
I have been reading about adding vinegar before watering. I would be worried about adding too much. I hope I can carry on using tap water with no bad effects.It will be interesting to hear your results.