I accidentally deleted your post in the Sick Cacti forum, so my sincerest apologies about that. Here's the relevant bit I snagged before I made the boo-boo:
When I was helping you with your Arios, we didn't have a chance to discuss the type of mix you're using, so let's do that now...Edwindwianto wrote: ↑Tue Jan 07, 2020 2:31 ami will re-pot it this saturday with fresh and dry substrate (coarse silica sand and lime stone)
Even though it's coarse, silica sand is not a good material for cactus mixes. The best mineral for that is pumice because it has the unique combination of open porosity and good moisture retention. Bonsai nurseries usually sell pumice, so if you have one in your area, find out if you can get it there. The climate in Bangkok is humid enough to grow your cacti in pure pumice. The only drawback is that you'll have to fertilize your cacti every time you water. If this is doable for you, I can guide you on the fertilizer aspect.
If you can't get pumice, your other options for the mineral are crushed granite poultry grit or calcined clay cat litter. Since the crushed granite/calcined litter don't retain moisture, you'll need to add some soil to the mix for good moisture retention so that the roots of your cacti can take up water. 3 parts mineral to 2 parts soil will give you a good mix, but be sure to mix it thoroughly before you repot. If you want to add limestone to the mix, it shouldn't be more than 5% of the overall mix.
A couple more things here. First, the mixes I'm recommending will be good for your Lophophora and your Arios. Second, my rule of thumb for repotting is to let the plants settle in for a week or two after you repot, then give them deep watering. If you have any more questions, please let me know.
