Nitrite spike calculator

Nitrite enters fish through the same gill chloride uptake channel that absorbs chloride from water. Adding sodium chloride floods the gill with chloride ions that compete for that channel — physically blocking nitrite from being absorbed. The mechanism is documented across aquaculture literature (Boyd, etc.) and is the standard reason commercial fish farms keep emergency salt on hand for nitrite events. Important: salt does NOT remove nitrite from the water. Only water changes do that. Salt buys gill protection while the bacterial colony catches up.

The 10:1 mass ratio is the targeted protective minimum: 10 mg of salt per 1 mg of nitrite. For a 1 ppm reading on a 20-gallon tank that works out to under a gram of salt — small enough that even sensitive species generally tolerate it. The 1 tsp / 5 gal dose is the hobby-standard heavier dose, intended for severe spikes (≥2 ppm) where you also want some general osmotic stress relief. The conservative dose is much heavier — closer to ~316 mg/L, vs ~10 mg/L for the targeted dose at 1 ppm nitrite. Use the conservative dose only when your tank does NOT contain shrimp, snails, Corydoras, kuhli loaches, or salt-sensitive plants. The calculator gates the conservative recommendation behind the salt-sensitive-species toggle.

The targeted 10:1 dose is small enough that most setups handle it without visible plant damage — a 1 ppm spike in a 20-gallon tank is under 1 gram of salt, well below the threshold that stresses most stem plants. The conservative 1 tsp / 5 gal dose is much heavier and IS plant-stressful, especially for sensitive species like vallisneria, anubias, and most carpeting plants. Freshwater shrimp (neocaridina, caridina) and snails (mystery, nerite, ramshorn) are intolerant of even moderate salt. Always toggle salt-sensitive species ON in the calculator if you have any of these.

It depends on whether your tank has cycled. If you're seeing nitrite at all, your second-stage bacteria (Nitrospira / Nitrobacter) haven't established yet — that's the entire reason this happens. From the start of the nitrite-spike phase, expect another 1-3 weeks before the colony catches up and processes nitrite to nitrate. During that window your job is to keep nitrite physically diluted (water changes) and gills protected (salt + Prime). Fish-in cycling commonly takes 4-6 weeks total; if you're at the nitrite phase, you're 2-3 weeks in.

Toggle salt-sensitive species ON. The shrimp are the limiting factor — you cannot use the 1 tsp / 5 gal dose without harming them. Use only the targeted 10:1 dose, which is small enough that shrimp generally tolerate it short-term, and lean harder on water changes to drop the nitrite. If nitrite stays above 1 ppm for more than 24 hours despite changes, the safest move is to temporarily relocate the shrimp (a bare bucket with an airstone for 24-48 hours is fine) so you can use a more aggressive treatment for the fish.

Methemoglobinemia. Nitrite oxidizes hemoglobin into methemoglobin, which can't carry oxygen. The fish suffocates internally even with plenty of dissolved oxygen in the water. Visible signs: chocolate-brown gill color (vs healthy red), gasping at the surface, lethargy, hanging at the bottom of the tank. By the time you see the brown gill color, the fish is already in serious distress. The two-pronged response (water change to dilute nitrite + salt to block further uptake) is the standard intervention; if available, an aquatic veterinarian may also recommend a methylene blue treatment. Most home tanks recover with the salt + water-change protocol alone.