Net water, not tank rating. Use the Tank Volume calculator if you have not measured it.
How much nitrate and phosphate your feeding puts in each week. Usually the real answer to a nutrient problem.
| Grams per day | NO₃ per week | PO₄ per week |
|---|---|---|
| 1 g | 7.86 | 0.907 |
| 3 g | 23.58 | 2.722 |
| 5 g | 39.29 | 4.536 |
| 10 g | 78.58 | 9.072 |
All the nitrogen in food ends up as nitrate unless something exports it first. Nothing is destroyed by filtration, it only changes form. A tank with climbing nitrate is either fed more than it exports or exporting less than it thinks.
NO₃ = 3.00 g dry × 45% protein × 7.0826 ÷ 284 L = 3.368 ppm/day
Crude protein on a guaranteed analysis is defined as measured nitrogen multiplied by 6.25, so dividing by 6.25 recovers the nitrogen exactly. That step is a definition, not an approximation.
That nitrogen becomes nitrate through the cycle at the fixed mass ratio NO₃ to N of 4.4266. Combining the two, one gram of 45 percent protein food releases 1 × 45 × 7.0826 = 319 mg of nitrate into the system.
Phosphate works the same way from the phosphorus figure, using the PO₄ to P ratio of 3.0661. Labels sometimes give phosphorus and sometimes phosphate, so check which before entering it.
Frozen foods are mostly water. Mysis is roughly 88 percent water, so ten grams of frozen cube is about 1.2 grams of dry matter. The calculation here applies the dry fraction before anything else, which is why frozen looks so much cleaner per gram than pellets.
Export efficiency is the honest unknown. A skimmer, macroalgae, and water changes together remove maybe 50 to 80 percent of what goes in on a well run system. Whatever is left accumulates, and that residue is what the nitrate trend actually measures.
The useful conclusion is usually about feeding rather than filtration. Weigh a week of food once. Most people are feeding two to four times what they believe, and no amount of media fixes an import problem.
Feeding less is not automatically better. Corals and fish need the input, and tanks starved to zero nutrients grow dinoflagellates and pale corals. The goal is matching export to a healthy feeding rate, not minimising food.
Sources: Dieck, Reef Chemistry Calculator