So I bought this Calathea about two weeks ago and the leafs were like that when I got it, however, for preventative measures, I'm wondering what causes these yellow spots on the leaf like that. Is it improper watering? Watering with tap water? Root issues? Or humidity issue? Has someone seen this in their Calatheas at home? How would you prevent this from happening in the future?
The two linear cracks on the bottom leaf are almost certainly caused by physical damage to the leaf. The pot may have tipped over and that leaf was caught underneath, or it may have been shoved to the back or side of a shelf and crushed against the wall. The other damage on that leaf probably happened at the same time.
The spots on the top leaf are more ambiguous, but since they resemble the spots on the bottom leaf, it seems likely that the cause is the same. Insect damage is not entirely out of the question, though. Keep an eye on the plant over the next few days and weeks, to see if any additional spots form.