You will want to use elemental advantage as much as you can, nevertheless, coz there's a mission every floor that requires you bringing elemental advantage. This basically means 1/3 of all missions. The brick we are talking about requires you to reach 10k points, which is exactly the number of points you can reach by clearing every single mission. That said, you get a few bonus points for clearing each floor in X turns, like 50 points for 0~4 turns, 40 points for 5~9 turns and so on. And what really makes for a bonus is the ranking afterwards. Well, I don't really want to go into depth about it, but anyway, you probably need to get about 8k points to be able to hit that 10k for brick after ranking bonus. For further information, google translate jp wiki here.. http://xn--hckqz0e9cygq471ahu9b.xn--...%20OF%20MALICE
There's so much time till tower, anyway, so just keep working on your grids - all your grids - and pray to RNG you get better water stuff.