Episode 41:
The hatsu lesson and water divination were in episode 41, right after the gyo lesson. In the manga, it was after the defeat of the Evil Trio. No major differences here, except the water was pouring normally in Gon's turn instead of trickling, and Zushi's leaf was staggering instead of little wiggles. A negative note here is the scene transition between the three turns. It was terrible the way they did and how it suddenly cuts with the nen vibration sound. And no rock-paper-scissors game either.
The old anime gave us a filler scene where Gon visits Wing on his own to show him his progress as well as asking him permission to fight Hisoka. Side note here, Wing tells Gon that he mastered water divination as if it was a special skill. That's not how it was meant to be in the manga.
Hisoka didn't have that outfit in the old anime either, but at least he got something on...!
Episode 44:
The results of the training were in episode 44, that's after Gon's fight with Hisoka and not before as the manga. The graduation scene was also after the results, but the old anime decided to make it after the final fight and was made as a real epilogue to the arc. And if you asked me, I liked it better. It had more emotions between the characters than the manga and the new anime.
The old anime didn't show this scene as well.
Episode 41:
Before going, Gon tries to tell Killua something ((after spanking his @$$)). This scene was not in the manga.
Hisoka's
boner erection joygasm excitement scene wasn't depicted as the manga, but you can still see "something" extends from him...!
The fight starts, and here's the first problem: The old anime kept using the same sound effects over and over again without any differentiation. As if the sfx library is so poor they don't have much variety in sound effects!
Some differences in the attacks. In the manga, Gon wasn't able to dodge Hisoka's rising kick, and his elbow strike hit Gon's chest instead of his face.
Animation recycling with visual effects
Hisoka's feint attack was a little different. In the old anime it came from underside instead of straight forward.
Gon didn't act as immature as here.
When Gon was trying to trick Hisoka, he moved fast in a way he created afterimages. In the old anime, he just delivers a punch before going to rip the stone tile off the floor.
The old anime made Gon punch the tile before kicking it. The manga and the new anime made him use the one kick only.
In the manga, Hisoka was wandering in his mind on Gon whereabouts. The old anime didn't show us that. In my opinion, this is important and it shows that Gon did indeed had Hisoka there and wasn't a lucky shot.
Overall, the fight was indeed nicely animated, but the changes in events and the technical issues made it lower in rates.