I am using Flora micro and Flora gro , 4 t5 's 7 inches away ph is always between 6.2 - 6.5 I check daily. Water temps varies 71 f - 78 f .

I also have these on a few of my lettuce plants left in an NFT system for 4 weeks without nutrient change. Changed the nutrients two days ago and added many plants. Will let you know if the new leaves improve or if the spots spread to other plants. I also have appropriate pH. I use CNS 17 hydro grow.
Upon further inspection of these,because of your post,I noticed some of my spots were actually silver, and some of these had small black spots in them- like eggs. Sure enough, spotted two tiny long bugs. Will look this up now. Hope you get more feedback soon.

We definitely have thrips. About three plants affected. This plant is the worst.

I have treated my affected plants with neem oil spray because I could not bare the options until I at least tried the neem oil. No bugs seem since treatment.
My lettuce varieties have nicely recovered, probably from a phosphorus deficiency when I didn't replace my nutrients soon enough. See picture, only the bottom older two leaves were affected.
Have you considered downy mildew? I am wondering if those spots could be the start of it?

I had lots of aphids this year and I used Eco Oil which got rid of them, I then got spider mites tint little spots under leaves used same treatment and fixed that problem.
I now have white butterflies who are laying eggs under my vegetable leaves , these turn into hungry green grubs that can be a real problem.
The fun never stops !

Hello,

It's potassium I think, maybe a bit phosphorous too. I had this identical problem with these spots too. It only happen's when I use a 3-2-2 never with 2-3-5 fertilizer.

This post was edited by Starling1992 on Fri, Jan 2, 15 at 10:03