They are the same chemicals that liquid ferts have but without the water mixed already. I see it as a matter of choice. One wants to have a bottle to pour "X" amount in per gallon which is quick and easy to figure but expensive. Another may have larger/more tanks and the dry ferts are simple once one gets the dose down pat. For dry ferts, I mix the powder into a small cup of water and pour it. I don't pay for water and shipping water. I feel I have better control with the dry as it is easy to vary the amount of each.