My sorority has been at a higher temp than I would like lately, somewhere around 83 or so. I like to keep my tanks around 78-79 if possible. The problem is... I don't have the instructions for my heater anymore and I cannot figure out how to get it to turn down. I tried twisting the blue part and it won't move. I tried moving the red arrow and it won't move. I tried twisting the black part and it won't move. I'm so stumped and feeling like an idiot, but if anyone can help me, I'd appreciate it. It's an Eheim Jager 75 watt heater.