problem?

1000wt light and fan vent. is wut my buddy is using.....he added just a little(like a third)of some bud boost from cash crop nuttes. only once......the only other nutes was bat quano 3 weeks ago......after that they got brown tips...so he tried to flush with some water.....he came back 2 hours later and the shit was fallin over he tied it up...and hour later 2 side branches started drooping and falling he cut one branch and tied one....what do you think tha problem is they are all 3 weeks flower

I think you are 'your buddy'. As for your problem, pfff far to vague info to diagnose at this point.

and the fan and some smaller leaves are curling downward but are still green, turning yellow from the middle out...from the bottom of the plant up

If they are curling down and yellowing inside to out then it sounds like necrosis brought on by a combination of factors you just need to find out which one. I would flush for a week, do not over water no nutes and make sure your ph is stable. If that doesnt work then report back.

thank you for tha answer..i appreciate it....i will let u know!! and I think Ph might be one of his problems too cuz he mix ph down in a gallon of water everytime...seems like he can't keep a steady ph cuz it could vary.....