(Apologies for minor schedule slip)

No Charmix
As Faragonda said while introducing Enchantix, Charmix was the goal for 2nd year fairies. So, it would stand to reason in S3 that the girls could call upon it when they really needed that extra boost. Back in the early going (after the first couple eps), I wrote up a bunch of predictions for S3, which included more Charmix and convergence use. One poster replied that it was too early in the season for such things, but I imagine that most fans would have expected to see them both eventually when things started to really heat up... and I suspect that viewers must have realized something was up when the Winx faced the Trix in episode 5 and still didn't use their Charmix :-/ (though a dub-induced plothole in that same battle may have overshadowed it)
IMO it didn't make sense for the Winx to simply abandon using Charmix without explanation, as not only was it the previous year's goal, but also unlike more recent abandoned transforms like Mythix or Tynix, one gets the impression that Charmix was meant for general use... so why not use them? :-/
(ETA: Seems like a Twitter user had the same thought as me, and tweeted about Charmix's total abandonment not just once, but twice :-))

No Charmix
As Faragonda said while introducing Enchantix, Charmix was the goal for 2nd year fairies. So, it would stand to reason in S3 that the girls could call upon it when they really needed that extra boost. Back in the early going (after the first couple eps), I wrote up a bunch of predictions for S3, which included more Charmix and convergence use. One poster replied that it was too early in the season for such things, but I imagine that most fans would have expected to see them both eventually when things started to really heat up... and I suspect that viewers must have realized something was up when the Winx faced the Trix in episode 5 and still didn't use their Charmix :-/ (though a dub-induced plothole in that same battle may have overshadowed it)
IMO it didn't make sense for the Winx to simply abandon using Charmix without explanation, as not only was it the previous year's goal, but also unlike more recent abandoned transforms like Mythix or Tynix, one gets the impression that Charmix was meant for general use... so why not use them? :-/
(ETA: Seems like a Twitter user had the same thought as me, and tweeted about Charmix's total abandonment not just once, but twice :-))