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    400w MH losing brightness after a few weeks?

    Hi, I have a 400w MH lamp with a magnetic ballast (400w). I remember when I first turned it on, about 3 weeks ago, I was astonished to see how bright it was and how well it lit up my grow box (mylar covered) - it was straining for the eyes to look inside the box. Now, 3 weeks later, it...