It is important to note that biofilters are more cost-effective in comparison with other types of purification, which is due to the low concentration of pollutants entering fish tanks to bred objects. The best filters of this type are structures of more than four meters and with a circulating liquid, having as the main material fiberglass, little susceptible to chemical environments and the effects of microorganisms, which determines its durability and performance. The principle of operation of such a filter is based on the purification of water through a material covered with a biofilm of microbial colonies. The study was conducted to determine the algorithm for digital prototyping and designing the biofilter capacity for pseudo-liquefied sand layers. The stages of setting and solving the problem are defined. The selection of the amount of biological sand loading is described using the equation for predicting total ammonium nitrogen in the system (TAN). To process 67 kg per day of extruded feed with 56 % protein, 5 m3 of quartz sand with a D10 size of 0.1–0.3 mm is required. The technology of 3D modeling used for designing buildings, structures and equipment is described. Modeling and rendering of the biofilter capacity can be performed in the SketchUp program. The principle of selecting sand for creating pseudo-liquefied layers is described. Prospects for further application of the technology are outlined. The research results presented in the article have shown that when predicting the release of total ammonium nitrogen (TAN), they help in solving problems with the conversion of fish and aquatic aquatic life products into nitrates, allowing you to select the sand layer in the required amount. Modern methods of mathematical modeling for designing for the development and use of fish-breeding equipment, which is actively used in agriculture, are proposed. In this case, it is necessary to take into account the idealization of the model by conducting empirical research at the stage of meaningful modeling.