The lower 70's gives Ich an opportunity. I'd go with 78 and up as well. Also keep in mind for those that are in the basement the temp. is now dropping, so be prepared to adjust your heaters just to stay at the same temperature.
Last week a club member had an Ich outbreak and we've figured the temp drop from outside and his maintaining a low 70 temp. contributed strongly to the outbreak.
80 on the nose for both my 20 & my 65. I was keeping them around 85 for a while to keep an ich outbreak from taking form...pleco caught it for sure but I raised the temp once I noticed it and never saw any other fish show symptoms....phew