My cousin recently gave me this cactus (succulent?) for my birthday, about a week and a half ago. It was apparently watered right before she picked it up, so I only watered it myself a week later. I looked online what to do so I soaked it in water, drained the excess, and let it sit. It's been living on my shelf right in front of an slightly shaded east-facing window, and I live in the Philippines so it gets lots of sun. I haven't touched it other than that time I watered it and to occasionally bring it down to say hi. But today I noticed a weird yellow fuzz growing on the base!! It's a thin layer of brownish-yellow something, kind of cakey. Might be mold?? I looked it up but I'm really not sure. Please help I'm really freaking out because I don't want to kill my cactus.
The only thing I can think of is too much water. Is the bottom part soft? If so, that's rot. Your only chance is to let it dry out till it gets better, but it may not survive. Cacti do not need to be watered a lot.
´Corking´ - or hardening of the skin is very common at the base of many cacti - plenty of mine exhibit it. Looks like the start of that to me. But still make sure your pot has a drain hole.
Earth has enough for man´s need, but not for man´s greed - Ghandi
Cacti are desert plants. When the weather gets cooler and the sun less intense train it to be outside. It can take the heat, you just have to bring it into shelter during monsoon season. https://www.youtube.com/watch?v=g6ur8YvQxKU
Happy gardening in Hawaii. Gardens are where people grow.