Backyard Aquaponics
A place to discuss aquaponics

Unsure if this is a calcium deficiency or something else?

I have it indoors and under a light, did not start getting these spots until plants had grown for 3 months.

I'm going to say its probably Magnesium or Potassium deficiency and not calcium. I'm assuming this is on older leaves since you said its been growing for 3 months. If in fact its on older leaves your noticing these spots, its because the newer leaves need the deficient element so it pulls it from the older leaves. Calcium is not mobile. Magnesium, potassium, nitrogen, phos, and others are mobile. How are your nitrate levels? What is your pH? Any other plants in the system with signs of dificiencies?


I'm still learning this stuff so I may be way off...

My guess would be anthracnose... See pdf here http://ausvegvic.com.au/pdf/VG10123_Let ... -Guide.pdf

You have signs of tip burn in your pics,so I will go with Calcium,I get this exactly the same look at times of high humidity,transpiration is low or nil resulting in low Calcium uptake,another sign for me is stubby roots,instead of the log white root system I normally see the roots are stunted and,well just don't look right.

It may be caused due to fungus. I've heard that lettuce should be grown with good air circulation and in case of appearance of spots it's better to rotate the crops. Will you be able to grow it outside??

I realize this is an old thread but I think it's probably either caused by calcium or guttation. Both of these look related because the water pressure within the leaf is involved. If too much water pressure exists you get guttation and water droplets along the leaf edge. When the water evaporates the salts left behind can cause tip burn. If too little water pressure exists then calcium doesn't get transported to the leaf tip causing tip burn. You might notice the guttation during the night or early morning.

Here's a good picture of guttation on a strawberry leaf - https://commons.wikimedia.org/wiki/File:Guttation_on_a_strawberry_leaf.jpg

Some miscelaneous related info -
http://purehydroponics.com/wp-content/uploads/2012/07/Avoiding-Tip-Burn-on-Hydroponic-Crops.pdf