Great questions. We are currently testing nutrients from several leading global companies, including some that are purely organic. We will be selecting a partner soon and will provide them in our individual capsules. They are designed to cover one grow. We recommend using the nutrients we provide, as we have spent large amounts of time matching the grow recipes to our nutrients to make sure that everyone using a Grobo can easily have the best results and can share grow recipes knowing they will work!
For all of the Grobo consumables, you should budget $15 - $20 per month. The nutrients (depending on what you are growing, and the quality of water that you put in the system) will typically need to be replaced every grow cycle (3-4 months). The carbon filter will need to be changed every 2~3 grows (6 to 9 months) and our coco coir is replaced each grow.
Hope this helps!