yup. thats exactly what it is. but dont worry too much, i dont wanna say thats an acceptable amount of nute burn becuase its never good....
it happens.
your recipe, or nutrient mix is just a smidge too strong. or
you fed them too much. or
your drainage is just a bit low. or
your pH varied a little
but you said it yourself, ¨they are very healthy¨, mine do that too, perhaps one shows it and another of the same strain doesnt.
one thing i do when i see that, is if i was watering them every 5 days for example, on the 4th day, ill come in and give them just a little pH´d water, then wait another day or 2 to feed again. that way they get a little less nutrient
guess you could just dilute it more too tho.
