He had to be at full power for the next battle, so they had to wait for the 24 hours to pass for him to get back everything. Since he couldn't use his TRANCE ROOM, which meant that this also was a Spirit-Based ability, he trained the old fashion way.
The floor's main mana was Dark Element, but it was too 'unpure' for one to use, so he couldn't train his Mana Tree. Even the Earth Element Mana was 'corrupted.'
So he decided to fulfill a task he had taken not too long ago; to learn a Base Grade Spell of each Basic Element.
He had Earth, Fire, Light, Water, and Dark cover and Spirit, but he wasn't sure if it was considered a Basic Element. So that left him with Air only, and luckily enough, one of his students had their Mana Pool being partial to Air Element. That was Mizuneko, of course.