Help with my Cory cats

[The603]

To answer a few questions, my tap water <10 PPM, they are mostly fed Omega One Catfish Pellets, and some Hikari Sinking Wafers. Going to try the plants and increased water changes route before adding aquarium salt which my other fish may not like or need until I do a little more research.
Thanks to all of you who have offered advice, and look forward to continue learning from all of you.