Saltwater Mixing Guide

How to Mix Saltwater for Your Aquarium

Good saltwater starts with clean water, a quality salt mix and an accurate salinity reading. Follow this simple process before adding newly mixed water to your aquarium.

Wet Pets Recommendation:

Start with RODI water, add the salt mix to the water, circulate until dissolved, verify salinity with a refractometer, then match the temperature to your aquarium before performing the water change.

1
Add RODI Start with clean water
2
Add Salt Salt goes into water
3
Circulate Mix thoroughly
4
Measure Check salinity
5
Adjust Correct if needed
6
Match Temp Then use it
1

Start With RODI Water

For reef aquariums, start with clean RODI water rather than relying on tap water. This gives you better control over what enters the aquarium and helps prevent unwanted contaminants from being added with each water change.

Fill a clean container with the amount of water you want to mix. Leave a little extra room so the water can circulate without spilling.

Need RODI Water Today? Wet Pets sells fresh RODI water by the gallon for customers who don't make their own water at home. Fresh Made RODI Water
IceCap 100 GPD RO/DI A practical home RO/DI system for producing purified water for reef aquariums, salt mixing and evaporation top-off. IceCap 100 GPD RO/DI System
IceCap 200 GPD RO/DI Higher daily production for larger aquariums or customers who regularly make larger amounts of RODI and saltwater. IceCap 200 GPD RO/DI System
Wet Pets RODI Options: Fresh RODI Water  ·  IceCap 100 GPD  ·  IceCap 200 GPD
2

Add the Salt Mix to the Water

Add the dry salt to the water while the water is circulating. Add it gradually instead of dumping the entire amount into one concentrated pile.

The amount of salt needed depends on how much water you are making, the salt mix being used and your desired salinity.

Not sure how much salt to add?

Enter the amount of water you are mixing and your target salinity into the Wet Pets Saltwater Mixing Calculator to determine how much salt mix you need.

Saltwater Mixing Calculator
Never add dry salt directly to an aquarium containing livestock. Dry salt can create extremely concentrated areas before it dissolves. Always mix new saltwater completely in a separate container first.
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Salt Mix Options at Wet Pets

Different salt mixes have somewhat different alkalinity, calcium and magnesium levels. Choose a quality mix that works well with the type of aquarium you maintain, then stay reasonably consistent.

Fritz RPM Reef Pro Mix A reef-focused salt mix suitable for mixed reef aquariums. Fritz Pro RPM Salt
Instant Ocean A widely used marine salt option suitable for general saltwater aquarium use. Instant Ocean Salt
Red Sea Salt A quality salt option for marine and reef aquariums. Red Sea Salt Mix
3

Circulate Until Fully Mixed

Use a small pump or powerhead to keep the water moving while the salt dissolves. Good circulation prevents highly concentrated areas and helps the mix dissolve evenly.

Follow the salt manufacturer's recommended mixing time. Some mixes are ready relatively quickly, while others benefit from additional circulation before use.

Don't judge the mix by appearance alone. Clear water does not automatically mean the salinity is correct. Always measure it before adding the new water to the aquarium.
4

Measure the Salinity

Once the salt is dissolved, measure the water with a properly calibrated refractometer.

Mixed Reef Target 1.025–1.026 SG Approximately 35 ppt
Best Practice Match the Tank Especially during routine water changes

For a normal water change, the new water should be close to the salinity already maintained in the aquarium. This helps avoid an unnecessary salinity swing.

Wet Pets Recommendation: Refractometer
5

Correct High or Low Salinity

If the new batch isn't at the desired salinity, correct it before adding the water to the aquarium.

If Salinity Is Too Low Add a small amount of additional salt mix, allow it to completely dissolve, then test again.
If Salinity Is Too High Add a small amount of RODI water, allow the batch to circulate, then test again.
Make small corrections. It is much easier to add a little more salt or RODI and re-test than to repeatedly overshoot the target in both directions.
6

Match the Temperature

Before performing a significant water change, bring the new saltwater reasonably close to the aquarium's temperature.

This is especially important with larger water changes where a large temperature difference could quickly alter the temperature of the aquarium.

Once the salinity is correct, the salt is fully dissolved and the temperature is appropriate, the water is ready to use.

Don't Want to Mix It Yourself?

Wet Pets also carries ready-to-use pre-mixed saltwater for local pickup. Always verify that its salinity is appropriate for your aquarium before performing a water change.

Wet Pets Pre-Mixed Saltwater

Storing Mixed Saltwater

Mixing extra water ahead of time can make routine water changes much easier.

Use a Clean Container Use a container dedicated to aquarium water and keep contaminants, soaps and household chemicals away from it.
Keep It Covered Cover the container to keep dust and debris out while following the salt manufacturer's storage recommendations.
Recheck Before Use Circulate the stored water and check salinity and temperature again before performing the water change.
Top off evaporation with freshwater — not saltwater. When aquarium water evaporates, the salt remains behind. Replacing evaporation with saltwater will slowly raise the aquarium's salinity. Use RODI water for normal evaporation top-off.
The Simple Wet Pets Method:

RODI Water → Add Salt → Circulate → Check Salinity → Correct if Needed → Match Temperature → Water Change

Open Saltwater Mixing Calculator

Always follow the specific mixing directions on the salt mix you are using. Different formulations can have different recommended mixing temperatures and times. For routine water changes, consistency is the goal: properly mixed water with salinity and temperature close to the aquarium helps minimize unnecessary stress on fish, corals and invertebrates.