Still others may enter the system as a result of the accumulation of organic matter such as insects or grass clippings. Once inside a system, the propagation of these microorganisms depends upon a variety of factors. The system must contain enough nutrients to sustain microbiological growth. The system must have the correct ratios of oxygen and carbon dioxide to support microbiological life. Tower location is an important factor.
Sunlight can significantly increase to a rate at which microorganisms propagate.
The system temperature must be within certain ranges for different types of microorganisms. Slime forming bacteria produce a dense, sticky mass which can cause fouling of system heat exchangers. Water flows can be impeded resulting in the loss of heat transfer. Additional microbiological growth is promoted when system water flow is reduced. Spore forming bacteria are difficult to control if a complete kill is required.