Hi
My calathea has suddenly developed a load of dark (translucent in light) spots on all the leaves. Is anyone able to help identify what the issue is?

Just to add to this, the brown spots actually appear translucent when you hold the leaves up to the light, with the spots visible on both sides of the leaves.

Is this just from watering with tap water? Is it some kind of bugs?

Any help is much appreciated.

Cheers