I have a few tomato plants growing in a wicking bed. They've been growing well up until a couple of weeks ago, when their growth started slowing dramatically. The leaves have begun to wither and curl upwards, and have taken on a slight brown/yellow hue. I initially thought they may be dehydrated, but increased watering hasn't helped. It may also be worth noting that they're sharing the pot with some chillies that began to grow very well around the same time the tomatoes started suffering. If you can recognise the problem here let me know!