I dont sale my treatment on Amazon, ebay only ( promoted listing with Purple&White capsule picture ).
As for the skimmer being off, You need to do it for 2 reasons :
1. Skimmer will remove medication you are about to add to your tank effectively making whole treatment a complete waste of time.
2. Skimmer will overflow with great amount of foam due to breakdown of any bacteria/algae = NO3 excessive build up & due to Fluconazole being present in the water in general.
Im advising to my customers to turn it off for entire treatment time ( 14-21 days). If you can remove the cup, then you can keep it ON for extra water flow ( oxygen delivery ), even then in some cases skimmers tend to overflow ( tanks were algae completely covered live rock ) through cup mount.
So if you will end up in the position :
a) You can remove cup & skimmer doesn't overflow = keep in ON at all times for extra water agitation.
b) Skimmer version doesn't allow to keep it ON without the cup = Leave it OFF for the whole treatment period.
c) Skimmer can stay ON without the cup but still overflows = as b)
Lastly, after 7 days, start monitoring your NO3 levels on daily basis, if it goes over 2, do water change (25%) and add more treatment calculating correct amount to compensate for water change L or Gal.
Best of luck