Can someone help me identify what's wrong ?

I'm growing 4 plants in DWC

The PH and temperatures of the water are in range
temperature is 20-22C, Ph is 5.9-6.0
Only one plant is showing this symptoms and I can't find out why

Appears to be a potassium deficiency or lockout.

PopAndSonGrows said:

Appears to be a potassium deficiency or lockout.

Click to expand...

So I can I fix it?

I'm feeding 3 part GH nutrients (Grow,Flora,Micro)

have you checked for root issues?

Mag or potasium lockout/def..
And nitrogen toxicity ..

Whats your water temp?? Looks like a root problem..