What Weaselcracker said.
One of the easiest things to do is to overfeed. First because it's so tempting to think that if two tsp/gal is good then 4 tsp/gal should be twice as good. NOT!. And the dosages on the manufactures' charts are really way too much IMHO. With nutes and cannabis, less is more. I use the FF regime and quickly found out the hard way that even an extra drop or two can cause distress in the plants.