its defenatly a blend of over watering and nute burn.....
First off, What kind of soil are you using?? if you havent been amending it with ferts, then its too rich for the plant at this stage...
and the 20 holes on the bottom of the pot arent gonnna help if they cannot evacuate the water..... You wanna come and punch a bunch of holes on the bottom sides of the pot... so that is can drain.....
your ph is fine seen as your between 6.3 and 6.5....
the white stuff, try and wipe it off with your finger and smell it after... Does it smell a little bit mushroom like.??? In that case its powedry mildew which you can treat with sulfur.... and garlic contains alot of it... so if you crush some garlic and mix it with water and spray that on.......
Otherwise you can make a baking soda mix.. and that will cause the leafs ph level to be unsuitable for the mildew to grow... make sure to cover the entire plant with it, over and under leafs... use 1 tea spoon of baking soda for 1 quart of water, and a few drops of liquid soap...
i highly prefer the garlic tho...
Good luck with that man!!
till that time, keep it greeen, in love and under JAH LIGHT