I am not sure what the cooling pads are, or how much liquid it circulates. But coils in the solution or visa versa may work. To be honest I am not sure if copper coils would react with the
nutrients at all, although it might add excess copper to the
nutrient solution. You can also use stainless steel tuning (very expensive), or any poly tubing (the smaller diameter the better). Although metal will give much better heat transfer. If using poly tubing you may need as much as 3 times as much as metal tubing for the same results.
P.S. If you had a link to the coiling pads that you were planing to use, and a simple diagram how you plan to use it, I could possibly help with refining it.