Saltwater Reef Aquariums and Trace Elements – the Truth

by Tom Lang

People are being sold a bill of goods. A bunch of hooey. A load of… Well, you get the picture.

Coming home from a consultation I had regarding a woman’s struggling reef aquarium the other day, I reflected on the nicely typed list that her local fish store had given her. It was not a list of things to do to maintain her aquarium properly, but rather a long list of additives they were telling her she must add to her aquarium water on a daily basis in order for her reef to live.

She was adding everything from “Essential Elements” to “Micro-vert Food” to “DNA Booster” and was adding capful after capful of these concoctions which cost anywhere from $20 to $35 a bottle.

Calculating the annual amount she would have to spend for these additives based on the fish store’s recommended daily dosages, I could certainly see why the store was motivated to keep her using these products.

Never mind that she didn’t need any of them. Never mind that their use was causing, not correcting, some chemical imbalances in her system.

After she followed my advice and stopped adding these “supplements”, her remaining living corals quickly became much healthier.

The fact is, based on published chemical assays conducted on freshly mixed synthetic seawater by Craig Bingman, Ph.D. and Marlin Atkinson, Ph.D. (1998) and others over the years, saltwater made using most major brands of aquarium salt (such as Instant Ocean) will actually contain greater quantities of trace elements than are found in natural seawater.

This is important to know because by adding more to these already elevated levels, the unsuspecting reef aquarium hobbyist is not only wasting money, but also creating a chemical soup that bears less and less resemblance to the chemistry of the real ocean in a very short amount of time.

Coral reefs are ecosystems even more diverse than terrestrial rainforests. They evolved over millions of years in incredibly stable, balanced environments. To be sure, there have been changes in the seas, but these have historically taken place over millennia. Most of the tropical marine fish and invertebrates we keep in our aquariums simply cannot tolerate chemical parameters that vary much outside of natural reef levels for very long.

But what are the important parameters? We know that coral skeletons contain every trace element found in seawater, but the major components are calcium and bicarbonates (Borneman, 2001). If we test for these in reef aquarium water, we find that calcium and bicarbonates are depleted rather rapidly. This is because corals use these major elements to build their calcium carbonate skeletons. Tests have shown that most other trace elements in our aquariums are rarely depleted from their already elevated levels and there is simply no need to supplement them.

If a calcium test indicates low calcium in the water, I simply mix the appropriate number of tablespoons of dry calcium chloride dihydrate (Dow’s Flakes – available at Home Depot and other sources) into 2 cups or less of tank water and add this solution to the sump or high-flow area away from corals after it dissolves. If an alkalinity test indicates low alkalinity, I add the appropriate number of tablespoons of Arm & Hammer Baking Soda dissolved into a separate cup or two of tank water to take care of the bicarbonates. It’s important to mix calcium and baking soda solutions separately and add them separately. A handy online calculator created by JDieck to determine dosages of calcium, alkalinity and magnesium is available here.

And how do I know how often and how much to add? By simply testing my reef aquarium water with a calcium test kit and an alkalinity test kit at least once a month (more often for reef aquariums heavily stocked with stony corals).

Since natural seawater around coral reefs contains anywhere from 380 – 450ppm calcium and has an alkalinity of around 2.8 millequivilents/liter or 8 dKH (Borneman, 2001), these are my target levels.

I have found that by raising my alkalinity a bit higher (3.5mEq/l or 10 dKH) with the baking soda, I can keep it from dropping below 2.8mEq/l over the course of a month as my corals grow and utilize the bicarbonate.

In my experience, this higher level is not so far off natural seawater to have any detriment. Again, in aquariums heavily stocked with stony corals, more frequent additions will be necessary.

Once the proper levels are achieved, it is fairly simple to figure maintenance levels of calcium and bicarbonate for any given aquarium based on regular test result trends. Every reef aquarium has different depletion rates based on what organisms are being kept and their collective uptake requirements for growth. It follows that the quantities of calcium and bicarbonates needed to maintain optimal levels might vary considerably from one reef aquarium to the next.

Hopefully the information in this article will help save you some money if you are keeping a reef aquarium. Even more importantly, however, you will have gained some insight into what is needed to keep the animals in your charge happy and healthy.


Atkinson, Marlin and Bingman, Craig. 1998. The Composition Of Several Synthetic Seawater Mixes. Aquarium Frontiers Online.

Borneman, Eric H. 2001. Aquarium Corals: Selection, Husbandry, and Natural History. T.F.H. Publications, Inc., Neptune City, NJ.

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