Some strains don't tolerate extremes in temperatures as well as others. What strain are you working with? Also, are you supplementing any CO2?

Temperature fluctuations used to be an issue for me, but I never noticed any major symptoms as long as the temperature was kept between 65-85 degrees Fahrenheit. Again, I've heard of some strains that can tolerate near freezing temperatures, and others that grow well in near 100 degree equatorial locations. So, I think it's really dependent on the strain.