I am helping a local head lettuce farmer. He grows head lettuce in high tunnels all year round, including the summer, in northeast Ohio. Not sure why he does this even in the warmer months, given that head lettuce likes cool weather. I know he uses liquid fish emulsion and sea kelp that he sprays around the base of the plant and on the plant. also he uses pelletized chicken manure, not sure how often. Soil feels very loose and has no quintessential soil smell (actinomycetes)
I noticed pink/discoloration on the leaves, more prominently in this variety but you can see a tiny bit of pinking on the variety to its right. Also, sometimes his lettuce taste salty and is brittle.
Any idea on what can be causing these problems?