Hy
grozyme, and most hydroponic stores will have it. If not, buy it online. It isn't inexpensive but unlike many products out there, it DELIVERS!
http://www.wormsway.com/detail.asp?sku=HYG405
Hygrozyme is an enzyme complex that takes any dead matter and digests it, making it available to the plant as food. Rot is stopped dead and the good tissue has a chance to take hold.
Same goes for Hydroguard:
Hydroguard Water Treatment
Hydroguard is a bacterial inoculant, the bacteria colonize the roots and water, preventing harmful pathogens from gaining a hold. This stuff is cheap though, and a little goes a long way.
My first couple of hydroponics systems were pretty poorly concieved, and with these I still got bud.