@silverdelange
what's up man,
yeah you got a typical fungus gnat there. eggs that was in the top 5cm of soil hatched. go check your pots for larvae in the top soil.
First off, is the plant healthy? A fully healthy plant should be "unfavourable" to insects, molds and diseases.
as for the spots on the leaves, I think you might be dealing with another kinda insect. mites or thrips.
2 ways to mend your soft bodied insect infestation that will benefit the plant also. Get 2 or 3 heaped table spoons of Diatomaceous Earth, sprinkle it on the top soil after watering as to not get it soaked, but have a dry layer of it on the top soil, can be mixed in lightly. The plant will benefit from the calcium, silica and other forms of nutrients the DE will add to the soil. This will kill the larvae and other insects that move around on the soil surface. Other way is to get some BioNeem and Pyrol, spray the Pyrol to help kill off the infestation, use the BioNeem on a weekly schedule to keep it under control. the plant benefits from the Neem oil ⁶helping it build a strong imune system so it can fight back against pests and diseases by itself.
NB - this can NOT be done during flower. hope you still vegging?