hrm... what is the environment like, temp, ventalitation? nutrient solution temp? lighting? Is there airation in the nutrient solution tank (air stones or circulation)?

Make sure the water level is reaching the roots, and It sounds like the air temperature in the growing area is very high, adjust the temp to about 75 degree Fahrenheit and you will see the difference.
SZ

Read here about hydro lettuce production

Here is a link that might be useful: Cornell Hydro

Thank you for the compliment.

Surprisingly, there is no algae. I started to get some in the watering bottle, so I trashed that idea. Originally, I was to use hemp mat, but it was next to impossible to find and the cost was other-worldly! The burlap works out to about a penny per tray.

All I do now is pour in enough water to wet the mat and slap a clear plastic dome on things and let it rip. The mat is wet all the time and stinks a bit at first, but as the lettuce gets about a half inch tall, the smell subsides. I haven't actually harvested or "tasted" any of the product yet, but my guess is it'll be just fine.

In between adding more nutrient solution, I foliar feed using nutrient at the proper EC in a spray bottle and lightly mist things every day or two.