Fish-food nitrate calculator
How much nitrate does feeding actually add? Daily grams in, mg NO₃ per litre per day out. The number your water-change schedule has to keep up with.
Stormy · the watcher
Food doesn't sneak into the tank quietly — every flake brings nitrogen. Stormy back-solves it from protein content: 16% of protein is nitrogen, every gram of nitrogen ends up as 4.43 g of nitrate once the filter is done with it.
Fill in tank volume, food per day, and protein % to see the daily NO₃ load.
How this works
Protein is about 16 % nitrogen by mass (the standard Kjeldahl convention, protein = N × 6.25). Fish retain roughly 30 % of dietary nitrogen in their bodies; the other ~70 % leaves as ammonia through gills, urine, and faeces. Your filter's nitrifying bacteria oxidise that ammonia to nitrate at a 4.43:1 mass ratio (NO₃ is 62 g/mol, N is 14 g/mol). The product of those four numbers is the daily NO₃ input from food.
mg NO₃/day = g_food × protein% × 0.16 × 4.43 × 0.70 × 1000Multiply grams of food by protein fraction by 0.16 (nitrogen-in-protein) by 4.43 (NO₃-per-N) by 0.70 (excretion fraction), then convert to milligrams. Divide by tank volume to get the daily concentration bump.
Caveat: the 0.70 excretion fraction is a typical middle value. Cold-water fish retain more, warm-water more active fish retain less. Plant uptake, denitrification in deep substrate, and any nitrate-absorbing media in your filter all subtract from this number — the calculator gives you the gross input, not the steady-state reading.
In the app, Manfred logs your real NO₃ tests and back-calculates your tank's actual consumption rate from the mass balance — feeding, dosing, and water changes all subtracted out.