I'm currently growing Tristar Everbearing strawberries in a big pot in my bedroom right beside a window. They got ample amounts of sun per day.

Recently, I've noticed that a few leaves have these dark greyish-black blotches on them. I wasn't sure what to do, so I pruned the affected leaves just in case. Can anyone give me any clue what it is/if I did the right thing?

Or better yet, if there's an organic spray I can make/use to get rid of it if it resurfaces.