First time grow and wondering about topping

Hi everyone,
Like the title says this is my first grow and I have a few questions about when and how to top my plants. I have 3 different strains, IE OG, Bubblegum, and Bubba Haze. They are clones and I've had them for about 25 days. I'm on a 18/6 light schedule under blue spectrum fluorescents, feeding with CES and growing in coca. The Bubblegum's are growing in very full and not very high however the IE and bubba's are quite tall and not as bushy as I would like. Anyway any advice you can give me would be greatly appreciated. Thank you all in advance.

get string and tie the plant side ways.. it will make all the other nods pop up and get bushy.. there is a post on here somewhere about LST. Low Stress something forgot the last word. im also new but have a few grows under my belt.. its work great for me with out stressing the plant. hope that helps

heres some pics of what mine are doing right now