Flowering plant showing signs of a deficiency?

Hi there,

This is my first time growing a plant and it is a little over 3 weeks into flowering in a grow tent with 2x300 watt LED lights. It has been doing great until the last 4-5 days I have been noticing some changes in the colour of some leaves. I will attach pictures, they look like brown rust-colored spots with the leaf eventually turning yellow. This is happening on the leaves mostly in the middle of the plant, not new growth or old growth. I’m not sure what it is since there are so many deficiencies but I’m thinking a calcium deficiency?

If so, what should I do? Do you think it’s possible I can just hold out until harvest?

Thanks, help would be appreciated.