This basil plant has strange spots (almost shiny?) and I can't figure them out

Question

I've been growing this basil plant for a couple of months. I started it from seed in a rockwool cube. Here's its environment:

• It's under full spectrum lighting for ~15 hours per day, and I recently switched from a 35W fluorescent to a 24W LED, both are designed for horticultural lighting. No sunlight unfortunately.
• It's been growing in a well aerated deep water cultivation fed by Botanicare Pure Blend Pro (the Grow 3-2-4 formula) at about 5ml per liter of water, as the bottle suggests.
• The nutrient solution has been completely replaced once, and that was a few weeks ago.
• It's in an apartment that varies between 22C and 26C, and the nutrient solution reservoir seems to stay between 23C and 24C.
• Relative humidity varies between 20% in the late afternoon and 80% in the morning.
• The system's pH is currently just above 5 (tough to get accurate readings with tester drops), which is where I adjusted it to after changing the nutrient solution, so it's steady.

Here's the plant next to its cilantro neighbor:

It's growing well, the leaves are fragrant and full, and I notice new growth every day. Happy days.

But I've noticed some light spots on the leaves that don't look healthy to me:

The first picture shows small light spots, and the second picture shows small dead spots that are actually a bit reflective/shiny. The affected leaves otherwise appear healthy, with good color and not even slightly wilted. Many leaves on the plant are affected, and the issue isn't localized in any one area of the plant.

I've looked very, very closely at affected leaves, unaffected leaves, the stem, the growing substrate, the surrounding area - there are no visible insects crawling or flying or worming around. I had a good look through some related threads (here, here, and several others that weren't related enough to link to), and decided to actually dissect a couple of leaves to look for leaf miners. But I saw nothing of the sort. Even with a magnifying glass, I saw no sign of anything alive. Nothing that looked like "trails" of eaten leaf. No bumps in the leaf or veins where they might be hanging out. No dark spots or anything that looked like frass.

What else could be causing those spots? Does anything listed in the plant's environment look out of wack?

Answer 1

We'll need more information of course. This could be nutrient deficiency; a few likely suspects are; copper, calcium, manganese, boron or magnesium or...thrips or even a virus. What is your pH? That is critical for your system. It should be 6.5. Lower will cause problems as well as higher for uptake in your system. My initial feeling are thrips...tiny dudes.

I am glad you looked for leaf miners. Do you have your air filtered?

Here is an excellent diagnosis link...it is for marijuana but I use it for everything.

leaf symptoms