Magnitude of temperature is less of a problem (unless you hit something like maybe 90) than the spike like Kien said. Even a tank can get whipped out if you temperature sits at 78 but you had a spike in a hour and BAM! I have kept my old tank between 81 to 83 so the temperature is not as issue. Probably you had a spike?
When something doesn't look good and I can't find any reason for that, I do WC
