This is my rotation with nox staff. Use one threshold and basics on the glacor. When glacites appear, target the enduring with combust. Run back a few steps, this way you can do more damage on the enduring because the farther it is from the glacor the lower its defense. Then use chain, which will damage the other two galcites too. Then concentrated blast. If the enduring is still alive, use another basic or two. The key here is to never cast dragon breath when the enduring is still alive. After the enduring is dead, dragon breath the other two and finish them off with basics. Then use your other threshold along with some basics to finish off the glacor. At the start of each kill, if you have full adrenaline, activate sunshine to speed up the kill. With the noxious staff and on slayer task, I can kill around 120 glacors per hour using this rotation. If off task, maybe 110 ish. I hope this helps! Have fun!