How Long Can Mixed Saltwater Be Stored?


This was a question that I asked myself many years ago when I was planning my latest build because I wanted to store both RO/DI water and mixed saltwater so I always have it on hand. Having access to either type of water can really save your aquarium and it did just that for me once already.

I had to do an emergency 50% water change a few years back because my tank suddenly went milky. Myself and a couple of reefing buddies put the cloudiness down to a chemical reaction within the water after my wife had used a really strong scented candle in the same room as the aquarium.

Again, this is our best guess because the candle made your throat sore and we had to ventilate that room. 3 hours later my water was going milky. Whether this was the culprit we will never know, but since then we are really careful about what airborne product we use in our house.

That incident motivated me to write an article to see if candles, scented oils and air fresheners are aquarium safe. You can find the link to that article at the bottom of this page.

Back to water storage, because I’d had the water stored and ready to go I was able to stop the impending tank crash. But the question is how long can water be stored safely?

How Long Can Mixed Saltwater Be Stored? – Tests have shown that mixed saltwater can be stored heated or cold with no detrimental effect for at least 3 weeks. Many aquarists report many months when it is heated and agitated with a pump when stored in a Food-Grade container with a lid.

If you are able to find the space to set up a container of at least clean RO/DI water then you have a good chance of saving your aquarium if an emergency arises.

Keeping a container of both RO/DI and mixed saltwater is even better.
Read on to find out how to keep your water.

Which Is Better For Aquariums: Natural Ocean Water Or Synthetic Salt Water

Natural Ocean water is a mix of many, many elements/ingredients that are not included with synthetic salt mixes. Many of these elements are organic and bacterial based organisms which could dramatically alter how natural seawater can be stored.

As with all living organisms, if the conditions to live are not provided they will die, decay and pollute the water.

Living Diatoms in Ocean Water Seen Under a Microscope

Not only do you have the living organisms within natural seawater, but you will also have many other elements/chemicals (You can tell I’m not a chemistry scientist!) in there which may breakdown or cause problems if left to stagnate.

There are not many people on the forums who regularly use natural seawater, let alone keep it for long periods of time, so trying to research this particular part of this blog has been difficult.

Most aquarists that use natural seawater only keep it stored for a week or two at the maximum. They always have easy access to clean ocean water so they never need to store it.

The best way I have found to store natural seawater is to place it in a container that allows sunlight to reach the water to allow the photosynthesizing organisms to live, keep the water heated at aquarium temperature of 78-80°F, keep it circulated using a powerhead or pump and to keep a lid on the container to prevent the ingress of dirt, dust, and debris from entering into the water.

This seems to be the normal way of temporarily storing water by the aquarists who use ocean water, but again, it’s not stored for long periods.

If you find the water has a foul odor, an oily residue or has a lot of floating debris or algae suspended in the water then it’s always best to dispose of it and get new.

Never risk your aquarium for a batch of water!

Synthetic Salt Water is a more controlled product containing only the good elements our tanks need to thrive and stay healthy. Because the synthetic salt brands have been engineered for our exact usage they store a lot better because they do not contain any pollutants or organic organisms that can die and decay.

The test data you will see later is based purely on synthetic salt brands as this is what 99% of the saltwater community use in their aquariums.

Are There Any Safe Saltwater Storage Containers?

Before we can even store water for any periods of time you need to ensure that the container or vessel you are storing that water in is safe for use and will not leach any toxins into the water over a prolonged period of time. What’s the point of keeping saltwater if the container is the problem!

Over the years I have seen many, many storage containers and some have been a major problem for aquarium owners because of the chemicals they have released into the water.

There is now a general consensus due to years of data from across the community that the following types of container are the best to use:

Any Food-Grade containers marked with ASF/ANSI 2 such as:


For more even more information on safe water storage containers, you can check out my article by Clicking HERE


Salt Brands Tested

The majority of salt brands used by most saltwater aquarists have been tested to plot the results you will see. The results are taken from the awesome tests the guys are Bulk Reef Supply conducted to test this theory once and for all.

The following salts mixes were used:-

  • Instant Ocean Standard
  • Instant Ocean Reef Crystals
  • Tropic Marin Classic
  • Tropic Marin Pro
  • Brightwell Neo Marine
  • HW Reefer
  • Red Sea Blue Bucket
  • Red Sea Coral Pro

Of these brands of salt mix, the Instant Ocean Reef Crystals and Red Sea Coral Pro are designed with elevated levels of Calcium and Alkalinity to help with the most demanding LPS and SPS aquariums.

Stored At Room Temperature & No Agitation

This is where most people would expect to see the biggest drops in Calcium and Alkalinity.

The salt was mixed and then left to sit in a closed storage vessel for 3 weeks.

No Heating and No Pump to circulate after the initial mixing of the salt.

Salt Brand1 Day1 Week3 Weeks
Instant Ocean
Standard
Alk: 10.3
Cal: 375
10.5
385
10.4
385
Instant Ocean
Reef Crystals
Alk: 10.8
Cal: 490
11.0
475
11.0
490
Tropic Marin
Classic
Alk: 8.9
Cal: 420
9.1
425
9.1
415
Tropic Marin
Pro
Alk: 7.0
Cal: 410
7.0
410
7.0
410
Brightwell
Neo Maine
Alk: 7.8
Cal: 385
7.7
380
7.8
400
HW ReeferAlk: 8.9
Cal: 425
8.9
420
8.8
425
Red Sea
Blue Bucket
Alk: 8.1
Cal: 410
8.2
420
7.3
410
Red Sea
Coral Pro
Alk: 11.2
Cal: 450
9.6
420
8.8
430

As you can see the test results for both Calcium and Alkalinity remained very stable over the three week period.
The only salt mix that had a significant drop in both the Alk and Cal are the Red Sea Coral Pro that was mentioned earlier.

Storing your water unheated and unagitated is proven to remain stable and of high quality.

Just be sure to heat and mix your water for 24 hours before adding it to your aquarium if stored in this manner!

Stored Heated & Agitated

Most aquarists, myself included like to keep their mix water constantly heated and agitated to ensure it is ready for use at a moment’s notice.

The second set of tests conducted by Bulk Reef Supply tested this theory to see if this way of storage affected the characteristics of the salt over a 2 week period.

The salt was mixed, heated and then left to sit in a closed storage vessel for 2 weeks this time rather than 3, but this time the heater and pump were left on 24/7.

Salt Brand1 Day1 Week2 Weeks
Instant Ocean
Standard
Alk: 10.3
Cal: 415
10.3
420
10.3
425
Instant Ocean
Reef Crystals
Alk: 10.8
Cal: 490
110.7
495
10.8
500
Tropic Marin
Classic
Alk: 9.5
Cal: 400
9.6
405
9.5
410
Tropic Marin
Pro
Alk: 7.2
Cal: 420
7.1
415
7.1
420
Brightwell
Neo Maine
Alk: 7.8
Cal: 380
7.6
395
7.8
400
HW ReeferAlk: 9.0
Cal: 430
9.1
430
9.3
430
Red Sea
Blue Bucket
Alk: 8.0
Cal: 410
8.0
420
8.1
410
Red Sea
Coral Pro
Alk: 12.1
Cal: 450
12.2
445
12.4
460

Again, you can see very little fluctuation in the test results over the two week period.

The main difference if for those of you that use the Red Sea Reefer Coral Pro salt is keeping it heated and agitated allows the salt mix to stay far more consistent over time.

Storing your water heated and agitated is proven to remain stable and of high quality.


Storing your water heated or cooled, agitated or not seems to make very little difference to the quality of the majority of salt mixes over time.

I personally keep Instant Ocean Reef Crystals for well over a month and every time I test it my results are bang on.

My recommendations are that you can store your water with no problems, just keep the container closed and check your parameters once in a while to ensure your storage system is keeping your water in perfect condition.

Richard – The Beginners Reef

Storing Saltwater Cost Comparison

Does your electricity cost you a fortune? Is running a pump and heater 24/7 not an option for you?

With the results showing very little difference between storing your water heated/mixed and room temp/sitting, a deciding factor could be how much it is costing you to have water ready at any time.

Heater Running Costs

Costs based on running ON and OFF but plugged in 24/7 and the US Average of $0.13/KWH as of Aug 2019. (50% on 50% off).

Wattage$ Per KWHCost Per
Week
Cost Per
Month
Cost Per
Year
50$0.13$0.55$2.18$26.21
100$0.13$1.10$4.36$52.42
150$0.13$1.65$6.54$78.63
200$0.13$2.20$8.72$104.84
300$0.13$3.30$13.08$157.26

Pump Running Costs

Costs based on running 24/7 and the US Average of $0.13/KWH as of Aug 2019.

Pump$ Per KWHCost Per
Week
Cost Per
Month
Cost Per
Year
MaxiJet 1200
20 Watts
$0.13$0.44$1.75$20.97
Sicce Silent 2.0
35 Watts
$0.13$0.76$3.06$36.69
Pan World 40PX
45 Watts
$0.13$0.98$3.93$47.17
Iwaki MD-20RT
58 Watts
$0.13$1.27$5.07$60.80

Therefore:

To run a 32 Gallon Brute Trashcan 24/7 with a 100W heater and a MaxiJet 1200 will cost you $47.18 in electricity each year to be able to have access to heated and mixed saltwater whenever you wish!

Tips To Aid In Safe Water Storage

  • Ensure your storage containers are Food-Safe Grade
  • Keep lids on your storage container but not air-tight
  • Check salinity every week for evaporation and replenish as necessary
  • Every 2-3 months empty and clean any residue in the storage container
  • From Instant Ocean Website:

    “Always allow newly mixed saltwater to circulate with a powerhead or air stone at least overnight before use. This allows the carbon dioxide in the aquarium water to reach equilibrium with the carbon dioxide in the atmosphere, which normalizes pH. It also adds oxygen.

    Stir vigorously to ensure a good mix. Although the Reef Crystals solution may be used immediately, we suggest aerating the water until it achieves oxygen/carbon dioxide equilibrium.”

Data Source

To view the extended versions of the above tests please check out the videos by the fantastic team at Bulk Reef Supply.

BRS Investigates Videos:

No Heating & No Agitation

Heated & Agitated 24/7

Further Reading

If you found this information helpful you may also like:

Richard

Hi, I'm Richard and I have been an avid aquarist for over 30 years with a passion for Saltwater Aquariums. I love to pass on my knowledge to help others get the same amount a pleasure out of this hobby as I do. View my About Me page to find out more about me & my mixed reef aquarium.

Recent Posts