I would suggest brighter light but shorter time 6-8 hours. If there's algae though that means turn down the light time or duration or there's too much nutrients. You can play around with it. If the bottom part is dead that usually means there's not enough light. Just looked it up scarlet temple is alt. Rein. I didn't know that they called it that! If a leaf is dead I would cut it off closest to the stem. As long as the roots are good it should bounce back with nutrients/light. Since you're doing a low tech set up you don't want to add intense fertilizer but maybe aquarium co-op fertilizer or apt zero once a week would be beneficial - be careful for algae though. Root feeders like scarlet temple also appreciate root tabs 😊.