my plants leave are curling down at the tips. I gave them a dose of Gnatrol WDG thinking it might be fungal gnats but that didn't seem to help much. The leaves straightened out some but still are curliing at the tips. any clues. I have been growing for 6 years now and I haven't changed anything such as soil food ect. this is the 3rd crop in a row that is doing this and the other 2 up and died on me 