Too late to return the Vipars? Look into the differences spectrum makes on the physical and chemical structure of your cannabis plants. You'll find the viparspectra 900 spectrum to be rather poor for cannabis, compared to a great many others.
You may want to look at adding supplemental lighting, to reduce the leafiness, or at least look at what you'll want to purchase next. The Mars Hydro TS series of lights is more toward the spectrum I'd advise, with them also being on the inexpensive end for pricing.