Corking? Or Trouble?

[7george]

There are plenty of fertilizers that give total NPK ''plus trace elements'' I would have no idea whether that contained Ca or not, Mg or not, B or not.

These always present in tap water so we don't need to add more even we always use rain or snow water. Sand and rocks in the mix contribute to these elements too.

Now, I do wonder if these adjustments and fine tunings are really necessary. I don't doubt your experience and success. But is anyone successfully growing cacti with off-the-shelf fertilisers? Or are most people doing some adjustments but never talk about it?

Yes, we do adjustments, intentionally or not. My tap water comes from a lake (reservoir) and lot of birds and animals contribute to nutrients' composition in that water. I use different inorganic fertilisers every other time: Scultz cactus (2-7-7 + Fe, Mn, Zn), RX 20-20-20 + Mn, Fe, Cu, Zn, Mo) and sometimes orchid food. In addition my soil mixes contain some organic content made from leaf mould and decomposed manure among other things.

[MikeInOz]

These always present in tap water so we don't need to add more even we always use rain or snow water.
Sand and rocks in the mix contribute to these elements too.

Unfortunately not true. Try telling a million dollar hydroponics set up that they don't need to add these elements because there's enough in the water.
This is especially true of my particular town water which is one of the most pure in the world and magnesium deficiency shows up within weeks (in fast growing plants) if it is not added in some form.
It's true that soil will contribute something if it is included. Sand and rock certainly will not do so.

[7george]

Well, I meant my case and my water mostly and the thing that I keep slow growing cacti mostly. Everyone should follow the most appropriate setup considering theirs case, plants and conditions. Ground water and that from rivers may contain significant amount of Ca and Mg carbonates.
Regarding the rocks under cacti roots: many believe all nutrients can be extracted from these degrading rocks (see "rock eaters" and associated topics in this forum).