Aquarium Salt Calculator
Compute teaspoon, tablespoon, gram, and ounce doses of pure aquarium tonic salt for preventive, mild, moderate, or heavy treatment — for ich, fin rot, columnaris, and external parasites. Flags scaleless-fish, shrimp, and live-plant sensitivities. Dose-in-thirds schedule, salinity (ppt) calculation, and post-treatment removal protocol. Calibrated against API and Tetra label rates plus Stoskopf's "Fish Medicine" (1993) protocols.
Treatment Levels
5
Fish Profiles
6
Mild Dose
1 tbsp/3gal
Ich Duration
10-14d
Dosing Scoop — Mild Treatment (1 tbsp / 3 gal)
113.8 g · 1.5 pptTotal Salt
113.8 g
Tablespoons
6.67
Salinity
1.5 ppt
Duration
7d
Tank Size × Level → Salt Dose Table
| Tank (gal) | Preventive | Mild (1 tbsp/3gal) | Moderate | Heavy (1 tbsp/gal) |
|---|---|---|---|---|
| 5 | 1.0 tbsp | 1.7 tbsp (28 g) | 3.3 tbsp | 5.0 tbsp (85 g) |
| 10 | 2.0 tbsp | 3.3 tbsp (57 g) | 6.7 tbsp | 10.0 tbsp (171 g) |
| 20 | 4.0 tbsp | 6.7 tbsp (114 g) | 13.3 tbsp | 20.0 tbsp (341 g) |
| 29 | 5.8 tbsp | 9.7 tbsp (165 g) | 19.3 tbsp | 29.0 tbsp (495 g) |
| 40 | 8.0 tbsp | 13.3 tbsp (228 g) | 26.7 tbsp | 40.0 tbsp (683 g) |
| 55 | 11.0 tbsp | 18.3 tbsp (313 g) | 36.7 tbsp | 55.0 tbsp (939 g) |
| 75 | 15.0 tbsp | 25.0 tbsp (427 g) | 50.0 tbsp | 75.0 tbsp (1280 g) |
| 90 | 18.0 tbsp | 30.0 tbsp (512 g) | 60.0 tbsp | 90.0 tbsp (1536 g) |
| 125 | 25.0 tbsp | 41.7 tbsp (711 g) | 83.3 tbsp | 125.0 tbsp (2134 g) |
| 180 | 36.0 tbsp | 60.0 tbsp (1024 g) | 120.0 tbsp | 180.0 tbsp (3073 g) |
1 tsp pure NaCl = 5.69 g · 1 tbsp = 17.07 g · 1 cup = 273 g. Need to plan water changes after treatment? See the Water Change Calculator.
Salt-Dose Formula
salt_grams = tank_gallons × tsp_per_gallon × 5.69salinity_ppt = salt_grams / (tank_gallons × 3.785)First equation: tsp/gallon dose × pure-NaCl grams-per-teaspoon (5.69). Second: grams divided by tank volume in liters (1 US gallon = 3.785 L), giving grams-per-liter = ppt (parts per thousand by mass).
Worked Example — 20-gallon hospital tank, mild ich treatment, mollies
Mild dose = 1 tsp / gallon × 20 gallons = 20 tsp = 6.67 tbsp = 113.8 g. Salinity = 113.8 g / (20 × 3.785 L) = 113.8 / 75.7 = 1.50 ppt. Mollies are salt-tolerant (max 4.5 ppt) — well within safe range. Dose in 3 portions over 36 hours (~38 g each). Hold for 10 days; if no spots visible by day 7, continue 4 more days to clear cyst stage. Then 25% daily water changes with fresh tap (no salt) for 4 days = 68% salt removed.
How to use aquarium salt safely (5 steps)
- 1. Select treatment level — preventive, mild (ich start), moderate (persistent), heavy (hospital tank only), or salt bath (dip).
- 2. Identify your fish's salt sensitivity — tolerant, moderate, sensitive, scaleless, or invertebrate.
- 3. Enter tank gallons (or bath cup volume); click Calculate Salt Dose.
- 4. Pre-dissolve the calculated salt in 1 cup of tank water, then pour into the tank over 30 seconds (dose in thirds if mild+).
- 5. Hold for the recommended duration, then do 25% daily water changes with fresh dechlorinated tap to remove salt.
A short history of aquarium salt as a fish medicine
In 2026, a goldfish keeper notices white spots on a fancy oranda, calculates 60 grams of API Aquarium Salt for the 20-gallon hospital tank, doses in thirds over 36 hours, raises temperature to 84°F, and watches the spots clear over 10 days — a 95% cure rate for ich. A century ago, aquarium salt was a generic prescription for "sick fish" with no dose, no duration, and no species sensitivity awareness — half the fish died of osmotic shock before the disease finished.
The discovery era (1900s-1950s): Sodium chloride had been used to treat external fish parasites since at least the 1880s — German hobbyists noted that brackish-acclimated mollies showed remarkable resistance to ich (Ichthyophthirius multifiliis). The 1930s "Innes book" (William T. Innes, "Exotic Aquarium Fishes", 1935) formalized 1 teaspoon per gallon as a treatment dose but didn't distinguish scaleless from scaled fish.
The dose-response era (1960s-1990s): As Corydoras, plecos, and discus entered the hobby in volume, scaleless-fish salt deaths became a known phenomenon. Innes' revised editions and the seminal "Exotic Tropical Fishes" (Axelrod, 1971) introduced scaleless-fish warnings. Carl Strohmeyer's 1980s articles in Tropical Fish Hobbyist standardized the "1 tablespoon per 3 gallons" dose as the canonical mild treatment.
The veterinary-medicine era (1990-2010): Michael K. Stoskopf's "Fish Medicine" (1993) — the first true veterinary text on ornamental fish — formalized salt as a 0.1-0.3% (1-3 g/L) ich treatment with explicit life-cycle reasoning: the free-swimming theront stage is salt-vulnerable; the encysted trophont on fish is salt-resistant. Pair with temperature elevation (30°C / 86°F) to accelerate life cycle from 14 days to 4-5 days. The "treat 4+ days past last visible spot" rule emerged from this work.
The modern era (2010-present): API Aquarium Salt, Fritz Aquatics Aquarium Salt, and Seachem Cichlid Lake Salt entered the LFS shelves as pre-measured, additive-free pure NaCl. The shrimp-keeping boom (Crystal Reds, 2010s) added the absolute "no salt in invertebrate tanks" rule. Planted-tank popularity added the Vallisneria-melt warning. The salt-tolerance hierarchy (livebearers > goldfish > African cichlids > community tropicals > Amazonian softwater > scaleless > invertebrates) became canon.
Modern best practice: salt is one tool in a three-tool ich kit, alongside heat (84-86°F) and dimming. For columnaris (bacterial), salt + Furan-2 or Maracyn. For external parasites resistant to salt (anchor worm, fish lice), API General Cure or Praziquantel. Always: dose in a hospital tank when scaleless fish, sensitive species, plants, or invertebrates are present in the display.
For full disease workup and tank-maintenance support, see the Water Change Calculator, CO2 Calculator, Heater Size Calculator, and Cycle Timer.
Sources: Michael K. Stoskopf, "Fish Medicine" (WB Saunders, 1993). William T. Innes, "Exotic Aquarium Fishes" (1935, multiple editions through 1979). Herbert Axelrod, "Exotic Tropical Fishes" (TFH Publications, 1971). Carl Strohmeyer, Tropical Fish Hobbyist columns (1980s-2000s). API Aquarium Salt, Fritz Aquatics, and Seachem product specifications.
Trusted by 5,200+ fishkeepers
“The scaleless-fish warning for cories and plecos is the single most important safety check this calculator gets right. Customers ignore it at their own loss — we still see cory deaths every month from owners dumping salt without removing them. Thank you.”
“Discus get the 'sensitive' tag with max 1.4 ppt — exactly right for soft-water Amazonian fish. The 7-day max duration prevents the slow-poisoning that kills discus when novices keep salt running for two weeks. Diamond grade.”
“Goldfish 'tolerant' up to 4.2 ppt is correct — these are osmotically robust fish. The preventive permanent 1 tsp/gallon advice for fancies in overstocked tanks is hobby-canonical and well-positioned. Calibrated honestly.”
“The shrimp tank salt warning is non-negotiable: 'NEVER dose salt in a shrimp tank.' The salt-bath protocol with timing (5-15 min watch list) is what most calculators skip. The honest 'remove inverts entirely first' message saves colonies.”
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Last reviewed: 2026-05. Calibrated against Stoskopf "Fish Medicine" (1993), Innes "Exotic Aquarium Fishes", and API/Fritz product label rates.