It's hard to tell from your pics, especially the one on the right. If you overfeed your plants, the signs of nute burn are pretty obvious. The leaves will show the nute burn on all the tips.

If your problem comes from overwatering, you may not want to flush your plants. If your soil does not drain well and you have been watering pretty frequently, I would let them dry out. Then water well with distilled water to clean out the potential salt built up in the soil. There really are so many possibilities, that it's hard to guess without knowing everything that you have been doing to them. Sometimes when a plant gives a problem, it's better to do less than more. Good Luck