Never had an issue, we raise hundreds of heads a year.

I live in the United States as well, but live in American Samoa, a US Territory south of the Equator in the Pacific Ocean about half way between Hawaii and New Zealand. We have a tropical climate, 80%+ relative humidity, with temperatures ranging from 78 - 92 degrees F. Have been growing non-circulating hydroponics lettuce commercially for about 10 months now but have always had problems w/ tipburn. about 25 days after putting 14 day old seedlings into my system, my romaine lettuce begins tip burn. my red leaf lettuce begins about day 18 after being transferred into my hydroponic system. have been using varieties purportedly tip burn resistant, but they all come down w/ TB. any advice?