www.youtube.com/watch
This will cover what we know about wavelengths and impact on plant growth as well as disspell some commonly held beliefs/myths. it's long. it's boring for some, but that's the best answer in regard to what part of spectrum does what.
i use the same spectrum from beginning to end. If i want to avoid stretching, i give more intense light - through dialing up power or shorter distance from light, it does not matter as long as rest of garden remains covered properly.
if the gnats are gone, i'd try to get back to normal. less pesticides the better. if you didn't follow a wet-dry cycle with your substrate, start doing so. this will help prevent gnats. let top 1" get dry - feel the weight of pot when wet and dry for another way to know when to water. Irrigate/fertilize with 20% runoff each time you do. Toss runoff on lawn or down the drain, but not back on your marijuana plants, nor let them sit in it. On top of keeping substrate at an optimal nutrient level, the dry portion of the cycle up top will limit pests.
neem oil is fine in vegetative phase, but never spray on flowers. An application lasts up to 2 weeks, if not mistaken. DE is awesome. it's like a wall to anything that doesn't fly... spread it around where it remains dry and not soemthing you'll step in or otherwise disturb as it will get messy and when wet doesn't function for pest control.
