For those reefers mixing small batches of saltwater and using it rather quickly after mixing, worrying about the Alkalinity and Calcium parameters shifting is typically not a concern.

A growing number of reefers are mixing large batches of saltwater, less frequently and use the water over longer periods of time or with an auto water change system. In these cases, knowing if your salt mix’s parameters are stable is important to ensure your tank is getting properly balanced water.

Will Alkalinity and Calcium levels in freshly mixed saltwater drop or precipitate during storage?

We tested our eight most popular salt mix brands:

We mixed 20 gallons of each salt mix brand to the most commonly targeted 35 parts per thousand (PPT) or 1.026 Specific Gravity. We recorded the calcium and alkalinity levels immediately after mixing and then at various increments thereafter up until 3 weeks from the date we initially mixed it.

We mixed each batch of saltwater until it was visibly clear at room temperature, then left it loosely sealed without any further water circulation or heat. The idea here was to eliminate the outside variables of water movement and heat, much like storing the water insidBrute trash can with a lid.

Something critical to note is that we tested our calcium and alkalinity levels using hobby grade test kits, just like you would at home and so granted a margin of error of +/- 0.5 dKh Alkalinity and +/- 10-15 parts per million (PPM) of calcium. This accuracy range and margin for error are within the test kit’s advertised range with some added room for minor procedural inconsistencies and subjective endpoint readings.

Changes in Calcium Levels

The changes in calcium levels don’t really tell a jaw dropping story when looking at the overall change for each salt mix and most are within our plus/minus 10-15 parts per million testing margin and some even tighter than that over the entire 3 weeks.

We don’t see a substantial drop in calcium due to precipitation presumably because calcium is more abundant in the water column compared to Alkalinity at roughly a 7:1 ratio. That means if the Alkalinity was to drop one full dKH, we would only see a change of 7 parts per million in calcium. Because of this, alkalinity readings will be a far better determining measure for gauging any substantial changes in water chemistry.

Changes in Alkalinity

When looking at alkalinity we see a clearer picture of how each salt holds up to storage because changes in dKH are more noticeable over any changes in Calcium.

We give this a 2 on the Reef Fantasy scale because it is pretty obvious that any of these salt mixes can be stored without any real issues, especially if left uncirculated and unheated as we did.

The only outlier in our survey is the Red Sea Coral Pro salt, showing the biggest change in levels throughout storage. We expected this result considering the high saturation of calcium and alkalinity levels and therefore propensity to precipitate and fall over time. Very likely why Red Sea specifically instructs you to mix for 2 hours ( no more than 4), heat the water and then use it.

You can expect reasonably stable levels through storage with any of the salt mixes we tested making them perfectly suitable for storage or use with an auto water exchange system in which the saltwater is used slowly over time. Keep the reservoir closed or covered to mitigate evaporation and out of any large temperature swings and pick a salt that matches your desired parameters.

Be sure to check out our complimentary BRS Investigates video in which we run the same test only with added heat and circulation throughout the storage and testing process.

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