Hi Scarab,
do you use carbon at the output of the skimmer ? Is it nec ?
According to Julian Sprung's book pg 131 ( don't know has it been proven wrong yet)
"Ozone was originally suggested to increase skimmer efficiency, but when larger amount is used, many of the organics usually extracted become oxidized into other forms that are more resistant to removal. Common symptoms of excessive ozone use are a dramatic drop in skimmer output, much lighter coloured effluent."