been using GH 3-part for year and a half and have never had spots like those. Nute mix i use is 5/5/5 (ml per gal of micro-grow-bloom mixed in that order in a gal water jug) during veg, half that for newly rooted clones, and 1 drp ST per gal. First 2 weeks of flower change to 5/2.5/10 and do not use ST during flower. starting 3rd week change to 5/0/10 until 2 weeks before harvest. at that point go 2.5/0/5 for 1 week and then 1 week of plain PH water. PH runs about 5.8 during entire grow.