Purple Urkle Clones

Started flowering light schedule yesterday. Plants really filled out last week. I probably waited just a tad too long since the tent is really crowded. I should be trimming I think but am unsure how and where. This plant is much different than the last plant... This is much bushier and crowded inside the bush. It looks like there are potential bud sites at bottom of plant well inside the canopy. I trimmed one such limb off because it was getting into the dirt. With my previous plant, it was much more obvious what to trim. I need to do more research I guess. I also noted that the top growth has a little yellowing of the very tips of the leaves. I don't know if this is an issue? See picture. Does anyone reading this (if anyone does) know? I also seem to have a small infestation of little black gnats (fungus gnats?) I saw one a few days ago and I bought some of the little yellow sticky cards to put in soil. I put one card in each plant. Since yesterday, I see about a dozen gnats on each card. Is this bad? Is there a safe insecticide I can use? I might try some Diatomaceous Earth powder on the soil.