water too warm?

so at first, i couldnt get my water above 71 even with my heater cranked all the way up. its been like 2 weeks since i first put it in and now my heater is on its lowest setting and its getting up there 79-80. is this too warm? i cant get it any lower. i switched to the lower setting a few days ago but still hasnt dropped any. its actually rising. it was only like 78 yesterday now its 80 and my heaters been on the lowest setting. its a 30 long. im scared if i let the heater keep running it will be at 82-84 by morning. the ambient temp in my room is only 65 and my heaters on the lowest setting at 72. Its a eheim jager 100w. What is going on?