it looks to me like your plants have got some sort of rot problem the best thing i can surguest for them is for you to take off all of the affected leaves and flush your plants for a week to make sure they have not got to much nutrient in them once this is done start feeding your plants again...
the best thing i have found for feeding cuttings , seedlings and young plants upon till they go in to flower is liquid light and saturator by dutch masters which you mix @ 60ml of each to 1ltr of water which has had a air pump in it for 24hrs to clean out all the crap that tap water contains...
you can use hydro nutrients in soil however it is not really recommended as the npk ratings of the nutrient for hydro use is different to that for soil if you are using hydro nutrients keep a very close eye on your ec levels as if you give the plant too much food :
A you may kill your plant
B...