nutrients from solution and convert the material to a biomass which can be utilized as a feed resource by shrimp and other demersal grazers it has been determined that some minerals in the water 22 become depleted during the shrimp culture cycle they have been found to become depleted in a fixed ratio relative to calcium in a preferred embodiment a dedicated selective ion electrode 64 is used to monitor calcium concentration in the water 22 the electrode 64 provides the input to a forward control feedback loop via the control unit 20 for the addition of a pre mix containing all the inorganics found to become depleted in a fixed ratio relative to calcium these elements include iodine strontium zinc calcium silicon and manganese by designing the tank 12 with a series of dividers 24 26 at fixed vertical intervals a culture tank 12 of almost any height can be built while the production efficiency based on volume remains essentially constant any decrease in efficiency as the number of decks 24 26 increases may be due mainly to the shrimp redistributing themselves on different levels to take advantage of feed introduction locations and oxygen gradients the multilayer approach illustrated in fig1 and 2 allows the indefinite expansion of the culture tank 12 in all three dimensions while maintaining the desired volumetric stocking efficiency a return spillway 66 at the top of the tank 12 may be used with the pump 14 which may be a small submerged draw pump to move the fluids and control flow velocity in the tank 12 based on the flow velocity of the pump 14 the flow of the water.