One thing that sets hydroponic systems far apart from soil-based growing systems is that the roots must receive as much attention, if not more, than the top of the plant throughout the growing process. Constantly inspect the health of the roots and the color, pH, smell and consistency of the growing medium.
If your hydroponic solution water is murky, has a bad sell, or is starting to foam when your additives should not have this effect, you have noxious microbe buildup. The root zone of your plants beneath the growing mat should be white, furry and growing vigorously. Brown, black or yellowed roots that are slimy and dying may be a sign of root rot. A lack of oxygen to the roots, improper temperature control and improper nutrient balance will also show as root death and/or stunted growth of the upper plant.
Cold temperatures inhibit water and nutrient uptake by the plants, while warm temperatures encourage microbe buildup. Microbe buildup in the solution and on the roots deprives the roots of oxygen, weakening the roots and stunting growth. Any time the roots are weakened, opportunistic pathogens attack the roots and flourish. The pathogens use up oxygen in their life cycle, further inhibiting root health. It is a quick and highly destructive cycle that requires acute attention to prevent.
Ideal root health requires temperature control, ideally between 68 and 72 degrees Fahrenheit, or approximately 20 degrees Celsius. Even short periods of heat or cold can cause major root damage. Ensure that your system provides adequate oxygen to the root zone. Use air pumps, air stones and/or H2O2 in the system. There's no such thing as too much oxygen in the root zones. Gradual addition of the correct amount of nutrients to the solution helps prevent shock or root death. Be sure to provide additives to your system that are designed to strengthen the roots, such as silica, H2O2 and beneficial microbes. Healthy roots resist attack from pathogens.
If the roots are already suffering from high concentrations of noxious microbes (cloudy, smelly or foamy nutrient solution), clean out your system. Rinse all roots and trim off dead root material. Treat your basins and reservoir with bleach or H2O2 solution, then rinse them thoroughly before returning the plants. If your plant roots lack oxygen, add air pumps or treat the solution with H2O2. Gradually bring your nutrient solution back to equilibrium if it has too much or too little nutrients.
Nutrient solution may discolor your root system, turning it yellow or brown. Certain varieties of plants and older plants may have cream-colored or yellower roots. Look for signs that the root system is still growing, is not mushy, and has furry-looking tips before worrying that your plant has root rot. Trying to keep your growing solution completely sterile is actually harder and often less effective than providing root-strengthening additives to your solution and maintaining a proper growing environment.