Can anyone tell me what this is?

Hello,

Can anyone tell me what this might be a sign of please, its the lower leaf i'm talking about, with the red arrow pointing to it.

Many thanks

It could be a nutrient deficiency or it could be mites.

looks like a calcium deficiency to me...

https://www.rollitup.org/marijuana-plant-problems/488004-guide-nutrient-deficiency-toxicity.html

^^ Look at the pictures of calcium deficiency...looks alot like your issues...

Check under leaf for little tiny spots or bugs/mites/thrips ... can use magnify glass or scope if needed

It does too, i was spraying them every for a week not so long ago to help with other cal def probs. So it could very well have come back in with different symptoms.

I have looked around for signs of mites but can't see anything at all under the leaves, spider mites have just killed off 2 of my chilli plants outside in the greenhouse, i hope i haven't brought them in!

I have just chopped 2 of the affected leaves off for a closer look.

There appears to be what looks like tiny hairs on the veins and stalk under the leaf, bearly visible in the photo but you can make them out. There is a close up of the front side too.

Thanks to those who have replied so far.