Several months ago I noticed black stains on the bottom and sides of my pool within hours of putting in Leslie's Power Powder. The pool was tested and showed some copper but no other metals. I Used Leslie's metal eliminator package (Stain Remover, Metal Free and Metal Curalotor packet) once the pool's chlorine level was less than .5 ppm as instructed. It has been several weeks with minimal change and the minute I again added Power Powder to re-chlorinate the pool the black spots began increasing. I found a post by onBalance, Senior Member and TPF Expert from 1-15-13 for a similar situation and he recommended using "potassium alum" granular (2-3 pounds) to remove the black stains quickly and vacuuming to remove waste and residue.
My pool is a 10,000 gallon, gunite, in-ground pool with a Haward filter and chlorinator. I have the following questions:
1. How much potassium alum should I use for a 10,000 gal pool?
2. How is it applied? Filter on or filter off?
3. What should the chlorine level be when I add the potassium alum?
4. Where can I purchase potassium alum granular.
5. Are there any precautions I need to take when using this chemical?