As an educated guess, I think he's getting more than 200 astral gems per turn with this nexus. Which probably has 500+ gems cast into it. And this is on top of him having twice as big gem income as everyone else.
I will of course join any gem pooling if we decide to continue. Just don't expect too much from my contribution - my astral income has been abysmal throughout the game and I would have to alchemize most of my gems to produce even a token amount of pearls for the effort.