It's well worth understanding the life cycle of pests in order to effectively attack them.

Thrips for example hatch in the soil, then the nymphs (little yellow/orange 'grain of rice' shaped buggers < 1mm) go and feed on the leaves, causing the spotting. After 3-10 days they turn into flying versions, breed and lay more eggs in the soil, flying ones last a few days.

I've been using nicotine to attack 'em - its like VX nerve gas for insects I've been spraying the plants and soil every other day and hardley see any now, but I know there are eggs waiting to hatch, so will contine for a week or two.