I have just begun DWC hydroponics. I feel I have ph and temperature at the ideal levels. My green beans, snap peas, and peppers seem to be coming along but my lettuce, tomatoes,onions, and herbs (tarragon, oregano,chives, and basil) are dying off or very limited growth. The lettuce, onions, chives seem to wilt and die, the tomato leaves start to shrivel and get brown on the edges and show stunted new growth. The plants are near a window and I have grow lights on from 6 PM until 6 AM daily. Some of the plants have root growth into the nutrient solution but they are few and probably not plentiful enough to nourish the plants. I would appreciate any help you can provide or recommend a source for me to research. Thanks in advance for any help you can provide.
Are all of those sharing a single water source? Some of these plants are not compatible with one another. Have you measured your E.C.? It sounds like they are experiencing nutrient burn from your description. Have you noticed a strange smell coming from your reservoir? There could be a fungal issue. Change your water at least 2 times a month. Weekly isn't necessary, but you will need to top off and keep the water level constant. If you let the water level go down, then you will find that the E.C. will sky rocket. This will cause nutrient burn. Any more information you can give will help me to help you better.
I recommend looking up companion planting charts to know which plants can share water, and which ones will not tolerate each other.