You don't want to dose GC and Metro at the same time. Because GC already contains metronidazole. This is how I would dose both medications:
Day 1: General Cure
*
Day 3: Metro
Day 5: Metro
Day 7: General Cure
*
Day 9: Metro
Day 11: Metro
* 6 days in-between GC dosages is usually suffice for clearing flukes. However, use this treatment calendar to determine when is the best time to add the second dose:
Marine Parasites
The treatment calendar takes water temp + salinity into consideration, which affects the worm's lifecycle.