It is sometimes assumed that because fungi have not been found in a fluid sample, none are present - and no fungicide is necessary. This is not the case. Fungi are almost always present in a fluid because they are commonly present in the air to which the fluid is exposed and they may also be introduced via water, tramp oil or a variety of other ways. However, they are usually fewer in number and less evenly distributed in the fluid than bacteria. As a result, contamination is difficult to accurately measure by conventional dipstick or plate count methods.
Fungi tend to grow on solid surfaces rather than suspended throughout the fluid.
Fungi that build up on splash areas, in troughs, on filters and in piping cause the most problems. Analysis of fluid samples does not reliably predict the level of fungal contamination throughout the system. Visual inspection coupled with quantitative measures is required to properly assess the degree of fungal contamination and the need for a fungicide. Some examples of species of each type are shown below. Molds can also form protective slime coatings and can develop large numbers of spores that serve to spread infestation.