Hi
@Crazydaver! You must fill in your reservoir with a new solution every 5~10 days to prevent any bacteria from developing and to refresh the nutrients for your plant... Changing it every 7 days makes sense, because you can adjust your feedings according to a weekly schedule. It's better to change it sooner rather than later, but once a week should suffice in most of the cases. Hope this will help, keep us up-to-date and happy growing 👊