How wonderful that your experiment turned out so well that you can barely keep up with it, that is a good thing. Swiss Chard always starts doing well again with cool weather, so you will get a lot more, I'm sure.
I have a suggestion for you. I use food grade Diatomaceous Earth to repel the insects and slugs. It does help and is safe to use for your food. Just sprinkle the powder occasionally around your plants and that should help. Otherwise, there is slug pellets that you could spread around the garden away from your plants. I use both and the eggshells too, Happy gardening!