In 1978, Lewis et al. sought to address the dilute nutrient issue. They worked with the
first recirculating aquaponic system, which was developed to operate with a high fish stocking
density. While the idea was good, nitrate concentrations were too low at 6–10 mg/L, and
producers were required to add a complete nutrient solution to support tomato growth. As a
general rule of thumb, nitrate levels should be around 46 mg/L. The low nitrate levels coupled
with high amounts of fish feed suggested that massive denitrification, or conversion of fertilizer
nitrate to nitrogen gas, was occurring and the nitrogen was being released into the atmosphere.