Dissolve one bottle cap of Root Protector in a quarter gallon of water (1 liter). Divide the solution evenly amongst the plants. Afterward rinse with plain water to spread the solution though the roots.
For the best results, use at the beginning of the light period. One bottle of Root Protector is enough for 20 large outdoor plants or 50 indoor plants. . Use a double dose for heavy infestations.
Haven’t personally used it but it is a root inocullant and in many applications the only way to get it to top of root ball would be to water it through I suspect that the purpose of pre-mixing is that it is concentrated and a bacterial culture. As culture it would have short shelf life once mixed in a dwc system I would use as directed pour through medium then lightly rinse and leave it in the system