I'm not a mod so take this for what it is worth. You need to worry about the algae bloom first. The staining you mention... Overnight? Common? Most stains are tannic acid. For me, earthworms and walnut bits (from squirrels in the area) do the damage, but it is strictly temporary. Being patient will work. The bleach will get them to vanish in a week or so, some times two or three weeks when I just open the pool. Have you been hitting it with heavy metals? Why do you asssume it is that?Are you sure FC 15? Is that holding? Had you just added sanitizer? Anyway, I should let the mods handle this, just wanted to try and insert stain-calmness.