What could be affecting my plants?

Theyes20

New Member
I have two plants that are about 4 feet tall and recently one has began to develop almost small spots on the leaves and they begin to yellow and die. I’m not sure if it’s some sort of deficiency. It’s an indoor grow and they get about 18 hours of light per day, the humidity stays around 55-60 and they both get balanced ph water and nutrients. Any help would be great, thank you.
 

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