Soil question

I started out using worm castings everything seems to be going well but 2 of the plants have weak stems should i let this be and wait and see wut happens or is there something i can do to fix this. Also im have about 6 plants using a 200watt floresent bulb should this be fine, im trying to start basic and not get anything serious until i need to or understand more of wut im doing cause im new at this. Also how often should i change the soil and i should use super bloom when it gets into the flowering stage, should i change the soil im using now maybe use something with more nutrients in it??

If you left yourself enough room you should add soil that way the stem is deeper in the soil and will be stronger. Also you may want to move youlights closer or go with stronger lighting if possible.

You cannot change the soil. Ya can transplant them into bigger pots with fresh soil.

Put a fan with a light breeze on them and the stalks will be fat.