The most common ways I see people 'doing it [dwc] wrong':
1) Using organics (including teas and molasses)
2) Using urea based synthetics like Jack's classic or miracle grow
3) Listening to advice to keep EC under 1.0. Not only will this cause deficiency, it makes your reservoir overly
hypotonic. Being in an overly hypotonic solution may cause the root tissue to become mushy. Think about what happens to your skin when you keep it in a fresh water pool for a few hours.
4) Not enough oxygen..
the essentials:
1) A proper balanced hydroponic formula based on calcium nitrate and potassium nitrate to source N rather than urea. EC should be between 1.0-1.4 at all times.
2) water
3) oxygen
bullshit:
silica, teas, anything with a rhino on it.