Nice pictures. Looks like "Little Gem" butter crunch. A simple "fix" to your anaerobic problem would be to toss an air stone into your nutrient reservoir and bubble air through it 24/7 using a small fish-tank air pump. A word to the wise: watch for ants in your growing area. They can bring in aphids and once aphids find the lettuce, it's either poison or the crop is history. I found out the hard way that aphids multiply faster than bunnies!

Anytime I have just one plant of any kind go downhill literally overnight, the culprit tends to be subterranean, and in my cases it's usually a mole who has dug through the roots. I'd check the ground for evidence of disturbance.

Aw. Naughty Jake. But in his doggie mind he was just having fun with something that had his favorite person's scent on it. You are a good dog mommy not to yell at him. I do think it is instinct. Rottie Shasta doesn't pull stuffing but she very carefully works the area with the squeaker until she can extract it. Sometimes it takes her days. LOL She uses surgical precision.

At least you are getting notice. Jail cells need plenty of tic before they are livable. You can go shopping for some nice bright patterned sheets, under-cot storage, a little Ikea desk and one of those cube storage systems for your clothes. And a few nice houseplants. Don't forget a little hand held bell so you can summon the jailer to bring you extra snacks when it is time for TV watching.