I've used the shultz before, but I realized that it has urea in it, unfortunetly so does the african violet stuff. They have better-gro at lowes now, it will be buy the orchids itself, at least it is here. The urea is for the plant to take out of the soil and use at a later time. Since the orchids don't have a "retaining" soil, it does no good. Um...other than that I can't tell you about the numbers. All I know is that they signify how much of phosphorus, nitrogen and magnesium. Well, I'm not sure that it is magnesium. I think that lja did say something about it in one of my questions. The 20-20-20 is different from the 10-10-10. Because when you dilute it to half strength, they have different ratios.