I know more about hydroponics than what these guys are doing, but you can compensate for mineral by adding them to your nutrients mixture (typical N-P-K) and wi

I know more about hydroponics than what these guys are doing, but you can compensate for mineral by adding them to your nutrients mixture (typical N-P-K) and will contain the 16 nutrients needed (Sulfur/Calcium/Magnesium/etc...). It comes in powders that you can just mix to your water.