Athosanswered grow question 6 years ago It is a slight nutrient burn.
When you say that you are feeding 0.6EC (PPM 300) that's total strength of the solution? Or plus water?
Second, feeding frequency. Even if you are feeding low strength, if you feed too often, that also can lead to nute burn. Feed only once every 7 to 10 days, no more in soil.
Third, sometimes plants react badly to foliar feedings, so don't do it.
Hope that helps.