Feed them more nutrients your PPM is to low. The spots are from nutrient deficiencies. Change your nutrients and start at 15 PPM. Your kannabis plants will grow even faster. If all is well in 2 to 3 days go up some more to at least 20 PPM. I know a grower with White Widow at 22 PPM and they grow like mad. Any lower and they show signs of nutrient deficiencies (same as the ones you mentioned)

If you have to much nutrients the tips of the leafs will burn and turn brown.

Good Growing!