What deficiency is this?

In fourth week of flower amd some leaves look like this

That's nitrogen deficiency there buddy! More info and pictures need.
What NPK ratio are you feeding them? How many leaves are like this and where are they located on the plant...etc

Jt0217 said:

In fourth week of flower amd some leaves look like this

Click to expand...

Looks like you have a potassium deficiency. During flower plants have a higher demand for phosphorus and potassium.