Which deficiency is this?

[Christine20]

Hey, guys,

In the flowering stage (in week 3 - 4) we confront with the same issue, let s say. I attached here a photo with some spots on the leaves. I read that this could be a potassium deficiency.
I have to mention that the girls are growing in clay pebbles & the Ph is 6.
Do you know what could cause this & how can it be solved?

 

[HydoDan]

Hard to tell anything from one leaf.
Need a pic of the whole plant and all grow info you can give.

 

[BigSco508]

Looks like a case of Pink Eye to me !

 

[PopAndSonGrows]

I'm gona say potassium? The way it's starting at the serrated leaf tips. . ...

 

[Christine20]

Hard to tell anything from one leaf.
Need a pic of the whole plant and all grow info you can give.

Here are some additional pics.

 

[Christine20]

Here are some additional pics.

I have to mention that we deal with fungus gnats. Can it be this a reason for the leaves looking like this? Also, we noticed that the roots started to get a brownish colour.