The floor has 2 colored quadrants (blue and red) and accordingly colored glass-tubes with fluid.
Fight the boss at the quadrant where he stands first. When one set of tubes runs out of colored fluid, move to the other quadrant.
You should be able to finish him here. if not, watch the tubes and move him back to his starting position.
The tubes slowly refill, so if you don't have good dps you will have to move between the 2 ever faster...
If a tube fully drains it will kill a player in the group and that tube will not refill, so if your DPS is low you should start moving him when the fluid passes the lower ring (he runs slow).