Heated and circulated premixed saltwater storage, how long will it last? - BRStv Investigates

April 30th, 2019
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We looked at the effects of heating and circulating premixed saltwater during storage by monitoring calcium and alkalinity levels over a 2 week period. We also observed the amount of precipitate leftover inside the container. We then compared the results with what we found previously during our BRS Investigates How long can I store saltwater after mixing? with the goal of providing you with the best methods for storing saltwater at home.


We aim to answer two questions: 


  • 1. Do parameters like alkalinity and calcium shift in heated and well circulated reservoirs?
  • 2. Will we see any related precipitation or crust in the bins after storage?


Saltwater Mixing Station


We all desire stable numbers for Alkalinity and Calcium and if given the choice we’d rather not have to adjust those levels in our mixing bins prior to using the saltwater for our regular water changes. 


Additionally, we look at precipitate in the containers after mixing in hopes of finding ways to reduce the amount of cleaning required to maintain storage reservoirs.


The Test Experiment


We tested our eight most popular salt mix brands that we also used in the previous test


We mixed 20 gallons of each salt mix with RO/DI water to the commonly targeted 35 parts per thousand (PPT) or 1.026 Specific Gravity.  


Finnex Heater and Maxi-Jet Pump


A 100 watt Finnex HPG Heater and Maxi-Jet 1200 water pump was placed inside each testing container to reach a target temperature of 78 degrees F and circulate the water inside. 


Some salt mix brands directly state to mix cold then heat to the desired temperature so we started at a room temp of around 68 degrees F and then slowly heated to a common target temperature of 78 degrees F over the course of the first 24 hours.  


BRStv Test Tanks


Each testing container was also loosely covered in plastic wrap to eliminate any debris from falling into the containers and reduce evaporation rates.  


Randy testing calcium with Red Sea Coral Pro Test Kit


We tested the calcium and alkalinity levels upon initial mixing and then in varying increments thereafter up to a maximum of two weeks using the same type of hobby grade test kits that many reefers use at home. 


We accounted for an accuracy margin in the test results of +/- 0.5 dKH for Alkalinity and +/- 15 parts per million(PPM) in calcium levels. This accuracy range is not only within the test-kits’ advertised accuracy range, but also adds some room for minor human inconsistencies and somewhat subjective endpoint interpretations.  


The Results

In theory, the solubility of calcium carbonate actually decreases as the solution temperature rises. Therefore, we expected more precipitate compared to unheated and uncirculated saltwater which we tested in a previous BRStv Investigates. The results here were surprising to say the least which we address after going through the test results.  


Calcium Test Results


Looking at calcium, in almost every case there is a steady line of stable levels for each salt mix with no drastic drops over the two weeks and actually a very slight increase in levels towards the end for a majority.


When interpreting the results, we focus on the data taken at 24 Hours to 2 Weeks because it takes up to 24 hours for the saltwater to be fully homogenized. 


We confirmed this by looking at the common trends in which all of the salts took somewhere between 6 and 24 hours to stabilize. 


Furthermore, this was made visually evident in another BRStv Investigates Video where we tested for clarity and contrast. All of the same salt mixes tested in this video required 8 or more hours to mix clear. Tropic Marin Pro being the best which mixed clear in about 8 hours and produced a stable 420 PPM of calcium after 24 hours.  


Tropic Marine Pro

Tropic Marin Pro

Change in Calcium levels when stored for two weeks

390ppm - 420ppm


Tropic Marin Classic

Tropic Marin Classic 

Change in Calcium levels when stored for two weeks

400ppm - 410ppm


Brightwell Aquatics Neo-Marine

Brightwell Aquatics Neo-Marine 

Change in Calcium levels when stored for two weeks

380ppm - 400ppm


HW Reefer

HW Reefer

Change in Calcium levels when stored for two weeks

No change - 430ppm


Red Sea Blue Bucket

Red Sea Blue Bucket 

Change in Calcium levels when stored for two weeks

420ppm - 430ppm


Red Sea Coral Pro

The Red Sea Coral Pro

Change in Calcium levels when stored for two weeks

450ppm - 460ppm


Instant Ocean Standard

Instant Ocean Standard

Change in Calcium levels when stored for two weeks 

415ppm - 425ppm


Instant Ocean Reef Crystals

Instant Ocean Reef Crystals

Change in Calcium levels when stored for two weeks

490ppm - 500ppm


None of the salts dropped like what we found in our first storage test. None of the tanks show signs of precipitate nearly to the degree we had at the end of our previous test (if any at all)!


Calcium Test Result Comparison


The most dramatic results show that with elevated salts like the Red Sea Coral Pro we can see a major difference in levels over weeks of storage. It is notable that the mixing procedure for Coral Pro explicitly states to mix it first, then heat as we have done, yet for this test we went well beyond the maximum 4hrs of mixing they advise. 


Alkalinity Test Results


Moving onto Alkalinity levels and comparing the same 24hr to 2week window the results show that each salt mix looks to be very stable across the board. 


Tropic Marin Pro

Tropic Marin Pro

Change in Alkalinity when stored for two weeks

7.1 - 7.2 dKH


Tropic Marine Classic

Tropic Marin Classic 

Change in Alkalinity when stored for two weeks

No Change - 9.5 dKH


Brightwell Aquatics NeoMarine Salt Mix

Brightwell Aquatics Neo-Marine 

Change in Alkalinity when stored for two weeks

No change - 7.8 dKH


HW Reefer

HW Reefer

Change in Alkalinity when stored for two weeks

9.0 - 9.3 dKH


Red Sea Blue Bucket Salt Mix

Red Sea Blue Bucket 

Change in Alkalinity when stored for two weeks

8.0 - 8.1 dKH


Red Sea Coral Pro Salt Mix

Red Sea Coral Pro

Change in Alkalinity when stored for two weeks

12.1 - 12.4 dKH


Instant Ocean Standard

Instant Ocean Standard 

Change in Alkalinity when stored for two weeks

No change - 10.3 dKH


Instant Ocean Reef Crystals

Instant Ocean Reef Crystals

Change in Alkalinity when stored for two weeks

No Change - 10.8dKH


Absolutely no denying the stability of carbonate hardness for all of the salt mixes with a majority staying very stable through the 2 week storage test.


Alkalinity Test Results Comparison


Again the elevated salt mixes having dramatically different results than previous tests without heat and circulation. 


Precipitate leftover in mixing container


Another interesting point is the Calcium Carbonate precipitate left over in the mixing containers was far less than what we saw previously which at face value kind of defies what we felt should be happening considering we added heat to the equation. 


Reef Fantasy Scale


Does the Alkalinity and Calcium parameters shift in heated and well circulated saltwater storage?

We give this a ONE on the reef fantasy scale, because the levels for both Alkalinity and Calcium remained very stable except for some slight increase in Calcium as the mix becomes completely dissolved. This minor increase in calcium could also be a result of using hobby grade test kits.


Did we notice any precipitation or crust in the bins after storage?

We definitely don’t see precipitate to the degree that we did in the first BRStv Investigates test in which the saltwater was stored without a heater or water pump. This begins to raise even more questions about why and how that may be and what we are actually seeing considering we know that heat will decrease the solubility of calcium carbonate in water.


Conclusion

Depending on the salt mix you use, it might be worthwhile to heat and circulate your saltwater during storage. Especially for salt mixes that contain elevated levels for reef tanks or clearly state in the instructions how to mix properly (Red Sea Coral Pro). That said, there are some salt options that maintain steady parameters and don’t require heating and circulating while being stored which equate to reduced electricity consumption.  


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