What's going on with my marijuana plant?

A question from a fellow grower:

I bought 3 seeds and planted them 1/6/15. Indoor. The Ph level has been
spot on as the oxygen. Plenty of lighting and temp is average of 71.
This is as tall as they’ve grown for 21 days now. Its as if they just
stopped. ? The other pic is some swag sativa that will easily out grow
the widow in 20 days. So any idea whats going on?

Plant size will be limited by the container size they are grown in. In the one picture you have too many plants in one way too small container, this is likely a significant contributor to limiting the size of the plants. The same is likely for the second picture, just way to small a container if you want the plant to get much bigger. Also you really should be only growing one plant per container almost regardless of the size of the container.