A brackish water salinity calculator helps you mix the right salt concentration for your aquarium. Brackish setups require precise salinity control — too low stresses marine-adapted fish, too high harms true freshwater species. Enter your tank details to get exact salt amounts, an SG/PPT conversion, and an acclimation schedule.
Tank Setup
Species Salinity Ranges
Results
Acclimation Timeline
Calculate to see acclimation schedule
Raise salinity by no more than SG 0.002 (3 PPT) per week to avoid stressing fish.
How to Use the Brackish Water Salinity Calculator
Setting up a brackish water aquarium requires more precision than a typical freshwater tank. Most brackish fish come from estuaries and river mouths where salinity changes with tides and seasons. Getting the salinity right for your specific species is essential for their health and longevity.
Step 1: Enter Your Tank Volume
Enter your tank's water volume — not just the tank capacity, but the actual water volume accounting for substrate, decorations, and equipment. A 20-gallon tank with 2 inches of substrate holds about 17–18 gallons of water. Toggle between gallons and liters to match your measurement system.
Step 2: Choose Your Salinity Unit and Values
Select whether you prefer working in specific gravity (SG) or parts per thousand (PPT). Specific gravity is measured with a hydrometer or refractometer and is the most common unit in the aquarium hobby. PPT (grams of salt per liter) is more scientific and equivalent to salinity in g/L. Enter your current water salinity and your target salinity — the calculator handles the conversion between units automatically.
Step 3: Select Your Salt Type
Marine salt mix contains additional trace elements, calcium, magnesium, and carbonate buffers that replicate natural seawater chemistry. Use marine salt for mid-to-high brackish (SG 1.008+) and for puffer species that benefit from complete ionic chemistry. Plain aquarium salt (sodium chloride) is adequate for low-end brackish species like mollies and gobies at SG 1.002–1.006 but lacks trace elements.
Acclimating Fish Safely
Never move fish directly from one salinity to another in a single step. The acclimation schedule shows you how to raise or lower salinity gradually over several weeks. The standard safe rate is SG 0.002 per week (about 3 PPT). Faster changes can cause osmotic stress, loss of appetite, and immune suppression. Always observe fish closely during any salinity transition and be ready to slow down if they show stress signs.
Measuring and Verifying Salinity
Use a calibrated refractometer for the most accurate readings. Swing-arm hydrometers are less accurate and prone to reading errors, especially with algae buildup on the arm. Calibrate your refractometer with reverse osmosis water before use. Always measure after mixing and temperature stabilizing — salinity readings change with water temperature.
Frequently Asked Questions
Is this brackish water salinity calculator free?
Yes, completely free with no signup required. All calculations run in your browser — your tank parameters are never sent to any server.
Is my data private?
Absolutely. Everything runs locally in your browser using JavaScript. No data you enter is transmitted or stored anywhere.
What is the difference between specific gravity (SG) and parts per thousand (PPT)?
Both measure salinity. Specific gravity compares water density to pure water at 4°C; pure freshwater is 1.000. Parts per thousand (PPT or g/L) measures dissolved salt by mass. Ocean water is about SG 1.025 or 35 PPT. Brackish water typically ranges from SG 1.002 to 1.022 or 3 to 30 PPT. This calculator converts between both units automatically.
What salinity is considered brackish water?
Brackish water falls between fresh (0 PPT) and marine (35 PPT). In the aquarium hobby, low-end brackish is SG 1.002–1.005 (3–7 PPT), mid-range is SG 1.005–1.015 (7–20 PPT), and high-end is SG 1.015–1.022 (20–29 PPT). The correct range depends entirely on the species you keep.
Which salt should I use for a brackish aquarium?
For low-end brackish species like mollies and gobies, standard aquarium salt (sodium chloride) works but lacks trace elements. For higher salinity brackish and puffers, a marine salt mix is much better as it replicates the full ionic composition of natural brackish and estuarine environments. Avoid table salt — it contains anti-caking agents.
What salinity do figure eight puffers need?
Figure eight puffers (Tetraodon biocellatus) thrive in low to mid-range brackish water, typically SG 1.005–1.008 (7–11 PPT). They can tolerate higher salinity but rarely do well long-term in pure freshwater. Always acclimate slowly when moving to a new salinity.
How do I acclimate fish to brackish water?
Acclimate slowly over several weeks rather than moving fish directly to the target salinity. Start at the salinity they came from and raise by no more than SG 0.002 (3 PPT) per week. The acclimation timeline in this calculator provides a week-by-week schedule based on your start and target salinities.
How accurate is the salt-to-water calculation?
The calculation is a starting point based on average values for common salt types. Actual results vary slightly by salt brand, water temperature, and dissolved minerals in your tap water. Always verify with a calibrated refractometer after mixing and adjust accordingly. Hydrometers are less accurate and not recommended for precise brackish setups.