Since they are growing in a substrate they will need to provide the nutrients to the plant, but one has to ask how do they know what to put each day? There is an arrogance to think they know exactly what the plant needs every day, especially considering that the plant’s need will change throughout the season. If they are practical, ask them to test the return water that comes out under the plant to see what not being used by the plant and flowing past the root zone. That is simple, straight forward, and pretty easy. If they aren’t on board for that they will never value a sap analysis.