You will need the person with Aggro to stay within melee range of Tert at all times. Tert will not move from where he stands from the two places he ports to and from. If he targets someone too far away he will ignite the docks and you will die. If you manage to jump into the water to avoid the fire you still will not be able to hit Tert and will need to die to start over.
Tert will port from one side of the docks to the side every 15-20% of his life you take away. You will need to have one tank group waiting on the opposite side for when he ports. Your DPS can swim across when he ports and continue to DPS him as long as they don't pull aggro from him while swimming across.
You will not be able to run around because the place where you entered from, the backside of the docks will be burning with blue fire the second you pull Tert.
Keep dealing with his porting back and forth and keep your two tank groups where they are to meet Tert when he ports to and fro.
Tert will run away 20% from dying and drain water around the docks. Quickly jump in the water and ride it down or you die as he sets the rest of the docks on fire.
Have each of your tank groups grab a turtle and pull them apart. If the turtles get too close it spell bad things for your raid. Burn one of the turtles down and then proceed to the other turtle.
Grats on your loot!
---------------------------------------------
Challenge Version
---------------------------------------------
The Challenge version of Tert is still about the same mechanics-wise to the normal version. It will be more important than ever to stay within melee range of the mob because on this fight the AOE's hit much much harder the farther away you are. Make sure the healers in the tank groups staying on either side are healing very well because they will take the most damage when Tert is on the opposite side to them.
The major difference aside from the enhanced damage from the AOE's and Physical attacks will be the presence of x4 crystals that will pop randomly around the spots that Tert spawns at. These crystals detonate themselves after a bit of time. The farther you are away from these crystals the more damage you will take. You will just need to heal through these crystals. They have way too much HP to worry about killing them. Just ignore them.
Kill tert the exact same way you do the Easy Mode version according to this strategy. Tert will still run away at 20%.
The biggest change will be the Turtles. The right turtle will need to be debuffed by Priests and the Left Turtle by Mages. To make sure you know which ones your classes are debuffing check the turtles before you engage them so you know who is debuffing who and what the debuff cycle is.
The turtles will slowly regen their life the longer you wait to kill them and will continue to regen throughout your fight with them. The turtles can not be more than 3% apart in their hp while you are killing them. If you have too much dps on one and not the other you will wipe. If someone dies, the turtle will heal and you will wipe. Assign two groups each to one turtle and burn them down. The turtles do have a nasty Power Drain every 60 seconds or so but is easily countered with good chanters.
You do still need to seperate them from eachother on the pull. If they are too close to eachother 5-10 seconds after they are pulled they will power up and wipe your raid.
Burn them out just like easy mode and grats on loot.