Hmm what could this ne now...?

Now this aint my first rodeo (lil southern joke there lol) but what in the hell is this.... Now i grow indoors. Water maybe every 4 days. i use soil. i believe it is a mix of MG organic and Hyponex. i have a 1000w MH and its in the second or third week of flowering. I use General Hydro ferts. i don't over water. I don't give too little nutes. nor do i over do it.... i noticed the beginning of gnats just starting. but gnats just starting wouldn't start this...? as you can see half of my room is fine. the other half is diseased looking lol. is it just me being paranoid or is this just my plants loosing nitrogen and getting more phosphorus... but if so why is it only half of my room.... i added pics. any feedback would be great to this confusing problem

When some plants flower they begin to kill off their lower fan leaves taking stored nutrients from them. Fungus gnats are a common problem with MG...I used to use MG. They shouldn't be too big of a problem, but they do nibble the roots causing some damage. Dry the soil thoroughly to kill them.

really? no one?

hmm. now when you say dry it. you are talking about full on drooping leaves dry? ive read that covering them in a layer of sand and possibly watering from the bottom would help... is this true or more fourm myth?