Here in Chile eating Tunas like any other normal fruit is very common. I don't like it, it has too many seeds and it's not that sweet, it tastes like cucumber. My grandmother has told me that people in rural areas used opuntis pads to purify water.

It was doing well, but I repotted it and a few weeks later it started developing this white thing I've looked online, but I can't figure out what it is. Any suggestions on what it is and how it can be treated?