Just as the waste nutrients of terrestrial fertilisers can stimulate harmful blooms of microalgae when they wash into aquatic environments, the nutrient-rich wastewater from open-system aquaculture operations can stimulate similar harmful eutrophication events, when not properly managed. The increasing implementation of indoor recirculating aquaculture systems (RASs) has been used as a solution to mitigate this issue for both marine and freshwater aquaculture. But it’s challenging to remove the excess nutrients – which would harm cultured fish – from the water before recirculation.