the 20-20-20 are percentiles, the fertalizer is 20% nitrogen ect, some ferts have much less ferts/inert ingredients and even though are exactly proportioned to the previous might only be 2%-2%-2%. all this means is you will be diluting the 20-20-20 much more, you could think of it like a can of soup and a can of condenced soup, 20-20-20 being more condenced, with the right amount of water both soups will taste the same, just follow the label and remember not to fert pot for first 30 days and only if it shows signs of needing some. then you should never go more than half what the directions tell you, pot is a weed and needs very little ferts compared to tomatoes and such.