No I haven't had to add anything besides chlorine in quite a bit. What chemistry would cause it to do so?This really sounds like a chemistry issue.... have you recently added anything to the pool besides chlorine?
Don't get hung up on that '12 hour turnover', there is no way to guarantee that every square inch of pool water has been filtered. For all we know your pump may only be drawing in the water immediately in front of the skimmer.
It would be a great help to see the pool water, could you post a picture or two?
I will take a few pics and post after work tonight.