We're doing the experiment above. We put the 2 gallons pool water in a clean bucket, waited one hour. Tested 0 fcl, 7.5 tcl, 7.5 ccl. Put ph up, mix, put hydrogen peroxide, mix, waited 1 hour, measured, fcl 0, tcl 5, ccl 5. We'll see what we get tonight after waiting 8 hours then tomorrow night after 24 hours.
Also, we're going to change the sand ( I had told my husband the other day that I thought maybe that was part of the problem since all of that junk was in the filter). I'm glad to know I'm not totally alone in my thinking! I'm also going to get the filter socks. I never heard of them before.
I'll post the results.