Got a Viparspectra 400w light lm301b diodes
Question is when to I reduce the light intensity and duration ?
Am currently on 18/6 cycle
Plants were 8 weeks old yesterday
Grandaddy purple feminized plants
Also I purchased a bloom fertilizer wondered if I should top dress before blooms start or wait till they begin to bloom ?
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Kinda depends on your space and need 
Got a whole plant pic??
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Welcome to the community , I would hold off on the Bloom products till after you flip to 12/12 Light schedule.
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At harvest you can turn it off. Otherwise, keep at 100%, raise / lower to maintain high PPFD 800 - 1000. Based on PAR maps it looks like 18 - 20". You can dial the light back the last 3 weeks or so if foxtailing is a concern.
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Ok thanks
Now can you clarify how I can determine when to reduce the light cycle and when do I dim my light output?
Thanks for the tips
Still learning here
One more question
When blooming begins should I remove the fan leaves ?
I see a lot of growers appear to remove those big leaves !
I only grew outdoors last year letting nature take its course no fertilizer only water !
All this indoor stuff is new to me !
Any advice is greatly appreciated !
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Fox tailing ??
Hi @Big-D if ceiling height is an issue, such as a tent grow with hanging lights then reduce your light schedule to 12/12 somewhere near when the plants can double in size and still not touch the lights. If your at 8 wks the plants have likely hit sexual maturity and could be flipped now. They will typically double in height during the flower phase. Good luck!!
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OK, @Big-D I’m one of those guys that don’t like to strip the plants of its leafs , I will take a few an tuck a few Throughout the grow to increase light penetration and air flow. I would crank the light up to full output when you feel like your space is full Flip to 12/12 light schedule to start flowering stage. just take into consideration the plant is going to double in size after flip.
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Someone explain what foxtailing means please ?
Not familiar with that terminology!
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OK, the last 2 or 3 weeks in flowering stage If lights are too intense you can But not always have a little Fox tailing. Pictures worth a 1000 words Google cannabis Fox tailing. It’s not something that I worry about. Good luck my friend ! 
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Ok thanks Kelly !
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It’s a simple math as when to flip to flowering. Just measure how much head space you have to work with, and measure how tall your plant is including the pot height. You’re going to want 15 to 20” space between the light and canopy, and your plant will approximately double in height when flipping to 12/12. So do the math and figure out how tall your plant can be in veg before flipping.
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