Rookie, please help!

[Sunny Oettel]

This is my first post. The tips of my lettuce, and other greens start getting dry and crispy, and the illness is working its way down, leaving dry crisp leaves.  They were doing so well before.  The greens are in two 2 by 4 foot trays of  raft system, that comes in play after two 2 by 4 foot ebb & flow trays. I have a 50 gallon tilapia tank with 9 small to medium Tilapia.  PPM is about 750, ammonia is less than 50, Nitrites are very low, Nitrates are good, pH is 5.9  My soy beans have spider mites. Please someone tell me what to do about my beautiful lettuce all going crispy.  Could it be the ppm is too high?  What can I do?  I just added the two ebb and flows to share the nutrients with more plants, hoping that would help.  Or could it be that I need to add aerators to the lettuce trays?   

[Brad]

Hmmm

I don't know have you had adverse temperatures lately. Sunburn will cause a darkening of the leaves which then dryes out. Freezing will burn tips but that is usually rot off.

Maybe this conversation will prompt some useful response.

 

[Jonathan Kadish NYC AA Chair]

Your PH is low and needs to be buffered up to or close to 7.0, but this probably doesn't solve your crispy lettuce. If you let the PH go much lower you run the risk of crashing your system. Post some pictures of the lettuce and maybe someone will recognize the issue.