Keep your plants healthy with good grow practices, and they will be less susceptible to pests and disease. Keep good air flow around the base of the plants, and keep your humidity down. Avoid splashing onto the leaves. A 'zyme' product keeps sloughed-off dead plant matter from causing problems, and peroxide treatments kill pathogens in teh res. Also I would look into Bacillus thurengensis as a potentially beneficial organism. I believe it is used to control insects in ponds and pools- might be worth a google...