If you're losing half your raid in the first minute of the encounter, it isn't because the encounter is overtuned. There are very serious problems with the raid in general if you aren't capable of surviving even that long. There isn't sufficient information provided to determine what the problems are for your raid.
On the boss turning...
The boss turns to cast Mutated Infection and Slime Spray. If you react to the wrong one, you may end up running right into the other. Slime Spray has a cast time, pay attention to the cast bar for the boss, if you don't see him casting, you don't have to move out of the way. The closer you are to the boss, the easier slime spray is to dodge, you have to move 2 yards to get out of the path instead of 10 yards. However, even if you're at range such as after a big ooze explosion, you can still avoid much of the slime spray if you are paying attention to it while you are running back in to the middle.
On the small oozes...
1. Everyone has to know where they are running out to before they run. If they run to the wrong side of the room, that's their fault. Look before you leap. You have 12 seconds to get out of the raid, that's plenty of time to figure out where you are going first before you drive halfway across the country in the wrong direction.
2. Never clense a person unless they are both moving in the right direction (towards the big ooze) and already out of the center. The dot ticking on the person even with the healing reduction debuff is still less to heal through than the aura of the slime on the entire raid. If they ran out of the raid the wrong way, don't clense them early either otherwise you just have a mob chasing them until they can get it merged.
3. No one is responsible for merging your slime except yourself. If you fail to merge the slime that spawns from you, that's your fault. No one can correct it for you. Learn from your mistake and stop repeating it. No one else can move your character for you.
4. You don't have to kite small oozes. Little wake up call, but a small ooze isn't going to kill you if your healing is sufficient for the encounter. For that matter, you will take damage regardless because you can't outrun it completely like you can with the big ooze. The first person to get it can simply wait for the second person to come out. They don't need to run around in a circle while the other person chases them. Just stand in place, wait for the second person, when they merge, both run back and the kiter takes over. If you can't merge the first two when there is nothing else going on in the encounter yet, your raid has absolutely no chance of completing this encounter.
"In anything, if you want to go from just a beginner to a pro, you need a montage." /w TankSpot WTB Montage for Raiders.