sand and perlite on top does not work. they find ways through air holes. ive done it all thats organic., azamax gognats, neem( great for pm), pure spray green(great for mites). What I found that works is oraganocide, and diatomaceous earth.....
aphids hang out at the bottom of the soil, gnats on top 2 inches of soil, trips , white flies, and mites hang out on the leaves. Pure spray will get rid of leaf dwellers after a couple applications. its omri listed too.
if you kill off your micros, just flush then dry then feed with compost or guano tea