Required aeration capacity is approximated to about 1 kw for 500 - 1000 kg shrimp or fish, though higher aeration efficiencies are obtained if growing conditions are optimal. Drainage of excessive sludge also raises aeration efficiency.
Water exchange in BFT ponds should be limited, both due to economics, environmental concerns and as a pre-requisite for the development of significant microbial community. Water exchange rates for intensive fish ponds (ca 10-50 kg fish/m3) should be up to 5-10% per day, whereas shrimp ponds carrying up to 2 kg/m3 can be managed with practically no water exchange, except for sludge drainage.
Feeding, C/N control
The microbial processes in the pond are controlled through the proper adjustment of feed application and feed composition, and control of the applied C/N ratio. Carbonaceous substrates are metabolized, about 50% of which are converted to microbial proteins accompanied by the immobilization of inorganic nitrogen, especially that of ammonium. It has to be noticed that some of the ammonium is removed by nitrification. A combination of nitrification and nitrogen assimilation by bacteria is more than welcome.
Carbonaceous substrates can be added in response to excessive inorganic nitrogen levels, at a rate of about 20 g carbonaceous substrate to remove 1 g nitrogen, as an integral part of feed application. To prevent excessive nitrogen build up C/N ratio of feed materials addition should be 15-20, though less carbon addition is needed if you got significant nitrification.
Many carbonaceous substrates can be used, such as wheat flour, corn or potato starch, cassava meal, molasses and others. Price considerations are valid, since there is no clear preference to any substrate. The substrate has to be finely ground or water dispersible so as to stay long in the water column. The carbonaceous substrate can be integrated with the normal feed pellets (giving the desired C/N ratio) or applied separately, as powder or molasses spread onto the water or as separate low protein pellets applied in addition to conventional feeds in separate application times.
It is quite easy to monitor total ammonia nitrogen (TAN) and other inorganic N species and to adjust the carbon addition so as to avoid excessive nitrogen or carbon application levels.