Purple Urkle Clones

Still struggling a little with the PM and the fungus gnats. Every once in a while, I'll see the white powder on a leaf/leaves and have to douse it with the Green Cleaner solution. Some spots seem to be stubborn to go away. Likewise with the damn gnats. They are reduced dramatically but still there. I'm not sure on the effectiveness of the diatomaceous earth. The gnats breed in the soil. So you put the DE on top of the soil...except.. there's no point in putting it on moist soil as it turns into white mud. The top of soil is dry for only a day or two between waterings and the next watering washes it away. So... Maybe.. You can get it on there for a day or or two between waterings. Is this going to be effective? I'm keeping up with the sticky cards but they keep showing insects in the tent. Not pleased about this. I trimmed the hell out of them yesterday. All major fan leaves are gone. I can see progress in bud growth but it just seems slow. Plants are using a little less water also. I can go at least 4 days between watering now. Every watering, I'm using about 2.5 gallons for both plants. I'm using nutes for every other watering. Not sure if this is correct or not. Directions from Fox Farms say to "feed twice a week". I water about twice a week. Should I use the nutes every watering?