Things You'll Need:
- Saltwater preparation
- Tap water
- Aquarium
- Hydrometer
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Step 1
Calculate the ratio of full-strength seawater to tap water that will provide the level of salinity required by your particular fish. For example, Rainbowfish might do well in 1/10 seawater. The ratio would therefore be 9 parts tap water to 1 part full-strength saltwater.
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Step 2
Prepare full-strength saltwater. Use a marine mix sea salt preparation designed specifically for aquarium use. Mix the preparation with tap water, according to the manufacturer's instructions.
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Step 3
Fill your aquarium with tap water to the level you previously calculator. For example, to create brackish water that is 1/10 seawater, fill the aquarium to 90 percent of its capacity as defined by the aquarium's manufacturer.
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Step 4
Add full-strength seawater in the proportion you previously calculated. To create 1/10 seawater, add 10 percent of the aquarium's listed capacity to the tap water already in the aquarium.
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Step 5
HydrometerIf you are preparing brackish water for a fish that requires an especially precise level of salinity, use a floating hydrometer to measure the water's salinity. Place the hydrometer in the tank and wait for it to settle. The water will cover the hydrometer to the level of the specific salinity of the water in the tank. Add or remove tap water and salt water until you reach the required level of salinity.
