i experienced low, but very thick, krausen. certainly no need for a blow-off tube.
that's the air temperature, unfortunately air isn't very efficient at transferring heat. so when the carboy heats up because of all the yeast activity, little heat will be carried away through the air. this results in the carboy heating up. water is a much better conductor of heat. put the carboy sit in a tub of water to which you can add ice, ice packs, frozen water bottles, etc (AKA a "swamp cooler").It's in my basement right now, which is measuring around 66 degrees.