What to do what to do

So I have been growing for awhile and although my plants are big they do not look as healthy as I would like I still have some yellowing and white tips also burnt looking tips. I have purchased a ph tester and I have been testing the water for about a month but I feel like they got worst. I give them pro grow and liquid karma also. I just put in a ventilation system today. Bu I didnt Think not enough air flow would cause so many issues. So my question for you wise growers is if the problems do not improve after reading Line after line about deficiencies, how do I get this right ?? When I think it is one thing something else goes wrong and I don't know how to fix this. I would love to get it right before flowering.

pics are your best friend

got some pics

Any suggestions people ??

some overwattering but i'm no expert have many problems of myself ... check this link http://www.weedfarmer.com/cannabis/plant_abuse_guide.php

Are the leaves curling? = Burn The yellowing could also be from lack of nitrogen since I had this one one and stepped up the nitrogen. Some people think MJ doesnt need Nitrogen while flowering, this is not true.