Not sure if i have root rot or my plants are rootbound, leaves are dying fast HELP

I am very experienced growing in tables with 40 plants and 2 lights above(1000 wt) now I am doing trees in big pots and all of a sudden in week 5 of bloom all the leaves are yellowing and dying fast. Everyday new dead leaves I have been sprAying growth plus and watering with sensizym and sub culture b. I have a fungus gnat problem hut I have gnats in tables before and they didnt do this.

Without pictures it's virtually impossible to help, post some pics, provide more information (PH, etc.) and then maybe somebody can provide some insight. Just on the surface it sounds like you are experiencing a nitrogen deficiency coupled with overwatering. Root rot is very possible, how big is a "big pot"?