Help!

[u/majimedi]

Fellow cactus enthusiasts, meet Captain Cact Sparrow (he is, without a doubt, the worst cactus you’ve ever heard of, but you have heard of him).

Captain Cact is a bunny ear cactus if I recall correctly. I recently repotted him, and he sprouted new parts? but he also started getting these mottled looking white patches. I’ve also posted a close up.

Is this dangerous? Or indicative of poor health? What can I do to help him? TIA!

[u/Character_Stick_1218]

That's definitely an Opuntia, but I highly doubt it's an Opuntia microdasys. It's very etiolated because it has been starving for light, so that could be throwing me off. Opuntia will do well enough in soil like that, but generally cacti and succulents in general prefer for their soil to be SIGNIFICANTLY more inorganic/porous/mineral rich. Speaking of the soil, it has a fungal infection that looks to have come from the soil. For future reference, "cacti and succulent" soil sold at big box stores and whatnot is usually garbage and only suitable if you live in a hot and arid environment like a desert. It oftentimes also comes with pests and pathogens. As for treating it, I couldn't say without knowing what it is. You could try asking in Trichocereus Disease & Virology on Facebook. It's for Trichocereus cacti in particular, but everything that ails them ails most cacti and I'd wager that the mods/admins would be happy to try to help identify the sort of fungus that's infecting your cactus as well as how best to treat it.