It looks like hard water marks to me.

If you can help it. Water from the bottom of the pot. Or let the water drain thru and out the bottom and try to leave the leaves dry. I have heard that milk on a towel will wipe off the discolors on the leaves and leave them shiny. Don't know this for sure.

Im new to all this plat stuff.. I just bought it last week, havent watered it yet.

It comes off if i wet it.

Could it be mealie bugs?. Does it leave a streak if you smash it? If not living, it is probably just hard water residue from a previous grower. It is harmless, although unsightly.

Mealie bugs, what the heck is that? I used a damp rag to remove the white stuff and its gone, I did not notice anything that can be smashed..

I don't think this is mealy bugs. looks like hard water or most likely it was water over the top with fertilizer mix. If it wiped off. Just check to see if it returns or any spots get bigger. Mealy bugs are about the size of a pin head, fluffy and can be smashed. But use a Q-tip and alcohol is better.
Stush

Just an update on the plant. I cleaned every single one and also repotted with 50/50 cactus mix and perlite. The white stuff hasnt come back so I think it was just what y'all said, hard water marks.

Should they be watered with rain water? I have a few buckets of that from yesterday's rain. Also how long should I wait to water it since I just repotted it.

Don't be in a hurry to water it. They need very little water untill the hot summer comes. It out side in a warm spot, you can water more. Some only water their plants once a month in the winter and just a little at that.
Stush

Thanks for tbe advice. So far it hasnt come back yet so must of been the hard water. I have not watered it in 2 weeks but I will in a few days. I was just curious if its ok to use rain water on them?

Unless it is dry, like the desert, I wouldn't water it (any Sans) yet. During the winter, or any time it's inside, pretend it's a cactus. It may take 3 weeks to dry out one time, 5 the next, a schedule is not usually very accurate, if one is trying to suit the needs of the plant. So many variables can wildly alter the rate at which the moisture is used/evaporated.

Rain water is always the best thing for plants, unless you have some type of "acid rain" although Sans don't have a reputation for being sensitive to tap water chemicals like fluoride or any of the chlorine/chloramine/chloride additives. Try not to pour any water into the "funnel" of the plant.

as purple says just like a cactus, but only in winter. i mist them occasionally though. and keep them in a sunny window: west or even south is best. they are from dry/wet season habitat - so they can withstand months without water. however, in summer time if you give them tropical humidity/hot temps you can water them to soaking and rundown on the bottom. that is the ONLY time i let the water run thru : but with sev small applications to saturate the rootball and allow slow absorption of water. so the roots are not clogged with water ever.
the marks on the leaves are likely from foliar feed at the nursery: it's very hard to remove them even with misting, sev careful wipes will do. nothing to worry about.
they like acidic soil, but do fine in neutral too. sometimes rainwater can be acidic aka 'acid rain' - so it's best to check the PH prior to use.
one more: plant them very shallow: 3" is fine even for big plants. leave half the pot unfilled and then put gravel on top - it'll stabilize the trunk and keep the pot from turning over.

Thanks for all the advice! I have done everything you all said. They are doing well (so far). I am keeping all of them inside except 1, which is a tiny one but my patio gets a lot of sun and I really want one out there because they are so cool looking!

Hope it's not direct sun, if so & it wasn't exposed gradually it may burn.

I disagree abt watering Sans. that infrequently (3 wks) or so now. I'd suggest observing the plant & checking the mix. I'm finding my mix bone dry, so I'm watering (some) of my Sans. every wk to 10 days or so.

You can use a chopstick or pencil to check for moisture. If still moist down below, some of the mix will stick to the chopstick.

I actually do not soil check mine - I just dribble some water every 7 days in winter and then the following day or two dribble some more. but mine are very densely potted and overgrown and old.
I grow them very hard. but give them a break in summer, when I give them some sun and humidity out on the balcony. then I even do sips until the water drips thru. and then let dry, but not completely. it's very different then: due to humidity they stay moist for a long time. so I give them more water, but even less often then in winter.

Pesticide. POSITIVE. I see it all the time. I work at Home Depot, ALL of our houseplants are coated in this. It's to prevent pest issues during transit mostly, when all those plants are crammed into trucks. I'm allergic to it, makes me sneeze SO bad, plus some itchy watter eyes and i get hives, couldn't figure out for the life of me until I was told that the houseplants I was happily playing in were covered in pesticide... If you bought this from a store, then I would say pesticide. It's nothing to worry about and will eventually wash off. The only other thing is hard water residue. I put some of my houseplants in the shower to water them and I DO get a white spotty residue on them but it's somewhat different than what is in that picture.