Here is a little info I found when I was going through this problem
Bacterial slime and other horrifying nasties
These are not the beneficial bacteria and fungi that we have already spoken about. These bacteria cause cloudy reservoirs, slimy build up, weird reservoir fuzz, gelatin growths and wild pH fluctuations. These are the reservoir monsters.
When these bad microbes are present at high populations and are happily feeding on organic matter, they use up just about all the oxygen in the nutrient solution, suffocating the plants. They release toxic substances as a biproduct of their life cycle. They also suppress the good microbes at the root zone and cause problems with nutrient uptake and plant growth.
Bacteria slime and cloudy reservoirs
Bacteria can make the water cloudy, but tend to produce more of a slime or jellylike, smelly mass in the system.If you have it, you will notice slimy reservoir walls and perhaps an oily slick on the water. Another symptom can be a foamy buildup in the reservoir. If left to their own devices, these bacterial growths will smother the roots, depriving them of oxygen. Some species of anaerobic bacteria thrive in an environment deprived of oxygen and can produce chemical metabolites, such as alcohols, aldehydes, phenols and ethylene, that are toxic to plant roots and to other microorganisms.
Other symptoms of bacterial infections can be fuzzy, cotton like growths, or the growth of fur. Just in case you are wondering, that white fuzzy growth you see at the tip of your roots is desireable. That is not bacteria - That is the good stuff - you should see tiny fine white hairs at the roots.
All of these nasties require organic matter to feed on. They may be there as the result of a buildup of dead roots and leaves in the root zone, but usually they are the result of adding an organic product to the reservoir. If the conditions are just right, the bacteria will begin to thrive.