Span Tabs: are used in your water bath/incubator environment’s to prevent many forms of algae’s, bacteria’s, and fungi from growing and infecting your research. Span Tabs come packaged in bottles of 75 blue tablets. How many tablets you use depends upon the size of the incubator/water bath. As the blue color fades you just drop-in another tablet! This saves you the expense of having to clean your baths out monthly, etc.