About the cause, the soil may be different before and after repotting. I also water my cacti thouroughly until water leaks out. How exactly did you repot? Maybe the soil you used now is worse than previously. If it is salvagable, the best thing to do now is unpot it and remove all the soil and let t...

Alright. I won't change my watering/fertilizing regimen. Thanks!

I also rotate my plants every now and then. Not 180 degrees though but 90 degrees. It keeps them from leaning

My Ferocactus herrerae is starting to bud. Are there special instructions for cacti with flower buds? Should I water or fertilize them more or should I just continue my regular regimen?

I can't vouch for neem. It didn't seem to help but it doesn't harm either.

I suspect they're dehydrating because of rotted roots. Can you use another material that's more airy? It looks like the one you are using would compact. Roots need air too. I use pumice that is 3-6ml big. And mix it with some organic potting mix because your cacti don't look like a desert variety.

If your potting mix has a lot of drainage, it would be fine to thoroughly water the pot because the mix wouldn't hold on to the water for a long time. It would also encourage the roots to branch out and fill the pot. But you also don't want to overwater. While you are figuring out the right watering...

What are you using? Is that sand?

It's great that you unpotted soon! I agree, it doesn't look like rot. Golden barrels don't dehydrate fast. I water mine once every 3 weeks or longer. Good that it's not squishy. How do you water it?

You shouldn't water cacti after repotting. Repotting damages the roots, which is normal, but you should let it heal before watering them. 1 or 2 weeks without water. Also, removing the old soil is good practice when repotting. Don't be afraid to break some roots. They heal and regenerate. I would un...

I have desert cacti and I use shade cloth when they get sunburned. If they can tolerate the sun, I don't use it.

I grow cacti for aesthetic reasons, not really to have a natural look. I also want a single big cactus rather than a cactus hidden by offsets. Some people like to leave the offsets, and it's cool, but it's just not my preference. My opinion is that removing the offsets would encourage the main cactu...

I buried my cactus deeper than it should and it was fine. I live in a humid climate.

I think it's safest to cut the top and root it. The problem with rot is it looks fine from the outside but the insides are dissolving. If you don't address the rot correctly, you'd end up with a dead and hollow cactus. If you bore its insides from the hole, you're hoping to remove all the rotted par...

I prefer a solo cactus myself. I just cut off the offsets and it is easier to done when the offsets are young. I don't really care about the offsets and just throw them away.