Have you checked out the Hydroponics forum here? I'm not sure but I think that may be your best source of info.

With in-ground plants few blooms is usually a sign of excess nitrogen fertilizer and that can also cause blossom drop so you might want to consider that possibility. Low levels of phosphorous can also contribute to poor blossom development but that usually isn't a problem with in-ground plants.

Dave

Here is a link that might be useful: Hydroponics Forum