I have a 26,000 gal in-ground pool with hayes filter and pump system. I put 3 trichlor tabs in each week plus chlorine bleach should my FC needs a boost and run my filter 8 hrs a day. My problem is I have developed 1/4" black spots on the bottom and I am sure it is not Black algae as I can't scratch it off of alter it in anyway even with a jack hammer, just kidding. I have read your posts and read about copper complications forming spots. I have a Flotron copper ionizer which has kept my pool algae free and chlorine consumption to a minimum. I love it, but now "me thinks" there is a relationship between the Flotron and the spots.
My pool stays balanced and crystal clear with the exception of my spots.