Our line of Agricultural, Chemical and Heavy-duty tanks are designed for use with fertilizers, chemicals and other liquids which require extra wall thickness to support the additional weight beyond what is required for water storage. Specific gravity is the ratio of the chemical weight per gallon divided by the weight of water per gallon (8.33 lb per gallon). Substances with a specific gravity greater than 1.0 are heavier than water, those with a specific gravity of less than 1.0 are lighter than water.