by the sound of things the tap water is the problem check the ppm of the tap water first as this will be added onto your 500ppm half strength solution so u could have like 800/900 ppm without realising. also if you check the ppm and ph of your dwc bucket daily you should eleveate the problem.

REMEMBER if you adjust the ph of the dwc bucket the ph will slowly level out over a period of time so dont add ph up/down untill you know the soloution is stable hope this helps.
(strains can change the ph when veging or flowering keep an eye on this)

As for your nutes i have recently changed from biobizz to b-a-c, and the difference in my plant after one day was amazing. im currently using soil because i havent the time or money at the moment to spend on a hydro setup, and also its easy to mess up so you have to be on it from day one till finish.(alot of hard work for alot of bud makes up for it).