Just keep emtying the collection cup on the skimmer and use some carbon. That will remove it just fine. The tea tree oil in the Melafix is what's affecting the skimmer and is making it produce excess foam in order to remove the foreign substance from the water.
Depending on why the LFS
recommended the Melafix, you may just want to turn off the skimmer and let the treatment run. Just ensure good surface aggitation to prevent the surface film from building up. Once the treatment is done, turn the skimmer back on coupled with the carbon and another water change should remove it in no time. Also ensure you clean water pumps and any loose plastic equipment well as the oil will adhere to it and linger.