A question from a fellow grower:
I started to grow indoor ive had my plants a 50% since day one they are growing but seem like if there taking for ever is there a way to boost up the grow speed and when do I turn the balast % upto 75
High ClaireILGM, you don’t say what make your ballast is, however I use a 600w Lumatek (dimmable) and being ‘dimmable’ I think that equates to what you’re asking. This is the one that I use and on the front you’ve a lumen control knob that adds on more lumens when turned full on - I use mine with it turned up full from the moment I switch it on.
This is the one I’ve got and you can see the front control. 
Hey ClaireILGM, I really need more information to give you an answer to your questions. I am not sure what you mean when you say “ive had my plants at 50% since day one”. I have to assume that you mean the setting on your ballast. If this is the case I put mine on 50% for new clones that have just came from under florescent lights for one day and raise it to 75% for one day and then 100%. This keeps them from being shocked if you are using a 600 or 1000 watt light. When you say it seems like they are taking forever to grow you need to be more specific. What is the rate of growth? Are they growing a half inch a day or are they growing a half inch a week? Does the new growth seem to be small? A lot of things can cause slow growth. How old are the plants? The environment: What is the temperature at the canopy of the plant? What is the humidity? How many hours of light are they getting? Nutrients could be an issue. What and when are you feeding them? Pictures would help a lot. Post the answers to these questions and I will try to help’
Thedinosaurman