Stains on new fiberglass pool

[TigerGalLE]

This is my first year with a fiberglass pool. We left it open because we enjoy looking at it. We don’t have too many trees but we have had some leaves and many bugs and worms. I’ve been running my SWG at night for about 8 hours. My FC usually hangs out around 6-7. My water is balanced otherwise. I have this light brown hue to my pool’s surface. You can see little white circles where worms and bugs have laid before I vacuumed them. Brushing and vacuuming doesn’t remove the stain.
Thoughts?

 

[TigerGalLE]

I just rubbed a vit C tablet on it and it works. I guess the treatment for this will be ascorbic acid. How do I prevent It from happening again?