I friend had the same problem them roots need some o2 asapo he took a pencil and randomely but carefully pushed it down in the soil to help it with o2 and dry it out a bit
I had 2 plants when I started now im down to one it died and looked just like that when I took it out of the pot I found root rot from over watering when I seen the picture I thought I was looking at my plant that died lol
to my knowledge general rule of thumb if sunthin says 6 months or aa year or which ever only count bout give or take half of what it says.. id say check your ppm's and check id say there low
right now im watering 3-5 days with nutes 2 times and the 3rd with noting but ph'ed water plus cal-mag plus and molasses and seems to be doing well as of right now I have never had to do a heavy based watering I mainly water till I get 10-15 percent run off slowly