Sorry. Fan girl slipped out.
And WOAH! 67ºF?! That's WAY too cold for one...you should definitely get a heater that works and get that temp up to around 76º-80ºF...
Fin rot is usually caused by poor water conditions. I suggest doing a 100% water change and take out any spiney plants that can further rip his fins (if they're plastic) and add aquarium salt to his water. OFL suggests 1 tsp aquarium salt per gallon of water for 7 days with 100% water changes. You need to keep the water "pristine" ... in other words, super duper clean.
Also, please answer these questions