Splat,
You have good light obviously because your internodes are tight.
But it is time to start feeding.
One thing I am seeing is that those plants look a little overwatered. Luckily they will be ready to repot very very soon, and when you repot them, mix even MORE perlite into your potting soil for better drainage. You may be also seeing a combination of low pH and wet soil. That yellowing and spotting is not JUST from the lack of nutes.