looks like nut lock to mee. could be fungus as well, another thing could be foiler spray burn. ph for hydro is supposed to be 5.8-6.3. any lower of higher and problems can come around. if spraying with neem or what ever, spray before the lights go out or when the lights are out, then shake the plants to get big drops off. for fungus a fungicide should be used how ever if in the roots it is usualy casused buy over watering, in this case letting the buckets dry out a bit and add some enzymes to the bucket. such as cannazym or hygrozym. botanicar also makes aproduct that can be good for roots called liquid karma, but its not the best for the price. canna then hyggrozym make the best. hygro also has a bottle for about 20 bucks now it is a limited 500ml bottle.