halfway
I understand not wanting to change anything half way (no pun intended) through a test. I just thought I would add some things to the discussion. I have been wanting to move to Alaska for decades, even wanting to start my hydroponic farming operation up there (haven't made it yet). But I am still always interested in anything about that state. It's well known that Alaska is the "land of the midnight sun" and grow very large produce due to their 20-22 hours of daylight.
I would agree completely with NorEastFla, that the stress factors are key to lettuce bolting. I did a little searching and found some things on growing lettuce in the land of the midnight sun. Keep in mind they refer to growing in soil not hydro, but they are talking about growing lettuce in nearly 24 hours a day of natural sunlight. I have not read them all, but what I have read the issues are dew to stress. There is some reference to length of light being a problem. But that's dew to higher
nutrient depletion from the soil in long daylight periods. That's a stress factor that can be easily remedied in hydro.
The Voice of Agriculture - American Farm Bureau
"Paul Huppert put down roots in Alaska and soon learned the secret behind growing tender good-tasting cabbage, broccoli, lettuce and potatoes. "Well actually, we have daylight practically all the time from mid-June on," said Huppert, the patriarch of four generations farming the rich Matanuska Valley. "We have 20-22 hours of sunlight and consequently that plant doesn't take a rest at night; it just keeps growing.""
""We can grow a crop of head lettuce in 60 days," says Huppert's neighbor, Ben VanderWeele. "The same crop of head lettuce, same variety, same everything, takes 90 days in the Salinas Valley in California, which is supposedly the best of the best.""
Alaska Mixed Vegetable Profile, in pdf.
http://www.uaf.edu/ces/publications-.../FGV-00040.pdf
"Although there are numerous difficulties involved in high latitude vegetable production, the 100-day growing season is augmented by long daylength, which allows for high production under irrigated systems."
"Head Lettuce production of 22,100 cartons were harvested from 52 acres in 2005. Average carton weight for Alaska grown head lettuce was 45 pounds, yielding approximately 497.25 tons of product"
"Sunlight is a major factor in crop production in sub-arctic Alaska with near-continuous light prevailing from mid-May through mid-July, followed by long but decreasing photoperiods through the end of the growing season."
http://www.uaf.edu/files/snras/C123.pdf
"Lettuce is susceptible to tipburn, a disorder where the edges of some inner leaves die from a localized lack of calcium that is related to uneven water transport. Water stress can lead to tipburn damage during the long days in June and July in Alaska." (nutrient and water stress problems can easily be avoided in hydro)
"Lettuce is sold in cartons that usually have 24 heads and weigh approximately 45 lb." (that's 24, 2 pound heads, heavier than what I usually get at the store)
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Here is a study on greenhouse production of tomato and different types of lettuce northeast of Fairbanks AK. There is some reference to using different cultivators for summer and winter in this ongoing study.
http://www.uaf.edu/files/snras/MP_09_10.pdf
P.S. I wouldn't go full strength with the nuts yet, for me the plants are still to small to make it worth it. I would stick to half strength for another week or two. I always quickly wash out the reservoir with a soapy sponge and rinse thoroughly, as well as clean the
pump and filter with each nutrient change. That makes it less likely for any pathogens to get a foot hold in the system (as well as any algae buildup). I also flush the system with plain water, then dump that before I add the fresh nuts. When my lettuce was just seedlings like that I went 3 weeks on 1/2 strength nuts, because plants that small don't take up much
nutrients at all in comparison to the later stages of growth. And the look of the nutrient solution was still a nice translucent color with no cloudiness. Also I was running low on my supply of nutrients so I wanted to stretch out how long they would last.