There must be adequate amount of spacing between the racks. While the idea here is to save on space, it does not mean you cramp everything up so that neither air nor light can penetrate. Also there’s a lot of plumbing involved in this process so you need to provide space for that as well - and make sure the space is enough for you to move in and fix any leaks or spills that might take place. This is very common because you’re working with a lot of water in this setup. You must also keep pruning the plants to make sure they don’t get overgrown and cover the whole setup.