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The importance of Calcium, electrolytes, a proper GH and KH in aquariums. - by Carl Strohmeyer

Many aquarists overlook the need for calcium, electrolytes, magnesium and the effect of a proper KH (Carbonate hardness) in their freshwater aquarium. KH is basically the buffering capacity of your aquarium, a Kh above 80 ppm helps prevent sudden drops in ph (You can convert dH [German hardness] ppm by multiplying your dH by 17.9). This is especially important with livebearers, goldfish, African cichlids, brackish and many other freshwater fish. The production of Nitrates (nitric acid) will slowly reduce your ph, but a proper KH will keep a more stable ph. This is important to note, if your KH is low and your ph has been dropping, a large water change (don't get me wrong, water changes are VERY important) can cause stress on your fish, or even kill them.


Another consideration of KH is that you can generally safely add the buffers (both freshwater and saltwater) that effect KH without sudden changes in chemistry (unless your KH is under 80 ppm already), unlike a direct ph or GH change. For this reason you do not always have to check your KH before adding buffers.
Baking Soda (Sodium Bi-Carbonate HCO3-), is often used for KH, Sodium Bi-Carbonate will buffer at 8.0 to 8.2. They are very good at buffering at that pH. Just a little Sodium Carbonate will absorb free H+ ions, and this causes alkalinity (which is the lack of H+ ions). To stop the Sodium Carbonate ions from consuming too much H+ and to keep a pH of 7.0 we need to restrict the amount of Baking Soda used, as it is always looking for H+ ions to consume. This is why I prefer using products that not only contain sodium carbonates (or sodium bi carbonates), but the proper ratios of other minor elements such as Calcium and Magnesium;
Sea Chem Buffer, or aragonite. The Sea Chem Buffer can be safely used for raising kH (& pH) in freshwater as well and is preferable and safer to baking soda, especially in community aquariums where baking soda can change pH too quickly, the added calcium and other elements keep a more stable pH and add necessary trace and minor elements (Of coarse, use in moderation in freshwater). Wonder Shells are an excellent compliment for raising Calcium, magnesium, and electrolyte levels quickly when used with aragonite or even Baking Soda, however by themselves they are poor for raising KH (great for GH though)


General hardness (GH) refers to the dissolved concentration primarily of calcium, magnesium and other mineral ions. Both Calcium and magnesium are important for proper internal osmotic processes in fish (and invertebrates). Other ions can contribute to water hardness but are usually insignificant and difficult to measure. When fish are said to prefer ``soft'' or ``hard'' water, it is GH, not the kH that is being referred to. GH will not directly affect pH although "hard" water is generally alkaline due to some interaction of GH and kH. A high GH in freshwater can cause respiration problems in fish, for a general freshwater aquarium a GH between 50-100 ppm is best (lower for Discus, higher for mollies/ African Cichlids).

Magnesium is important in SMALL quantities for proper osmotic functions in fish.
Magnesium is better added in the proper balance with calcium (which both are essential to each other for proper utilization), in such products as Wonder Shells or aragonite sand in a small bag in the filter (although the later is not as reliable).

Wonder Shells are useful for raising GH in general aquariums (tanks which prefer pH in the range of 7.0-7.8), as they do add more calcium and less of the other hard elements that are not beneficial.

A proper GH and electrolyte level can also have a positive effect on the aquarium Redox Potential, which recent studies have shown to be more important to fish and other animal health than pH. Proper electrolyte balance contributes to the Redox reduction potential of water, maintaining a more stable water environment, better clarity and the excess electrons attach themselves to free radicals, improving disease resistance.


Calcium carbonate in your aquarium will keep a more stable electrolyte balance (for osmotic function), while magnesium is another important element that works with calcium. A proper amount of Calcium and Magnesium in your aquarium will affect the fish health positively. Magnesium and calcium have been shown to increase resistance to degenerate diseases by lowering the acidity in the body. This will help with prevention of ich, fungus, and general “wear and tear” in your fish. Calcium also helps in healing and stress, and without proper calcium levels healing may be difficult or impossible. The addition of antibiotics (such as Tetracycline) will lower calcium absorption.
Another note about calcium; Calcium is very important to proper discus health, yet calcium can adversely affect the kH of a discus aquarium when combined with sodium carbonates or bi carbonates, which is generally kept at a pH below 6.5. I have successfully used calcium (Wonder Shells or Calcium Polygluconate) in discus aquariums by using a mix of RO (Reverse Osmosis) water and tap water (dilution will vary depending on your tap and tank water parameters). I then add electrolytes to the RO water and add peat to the filters. I have used this method successfully with discus and added the needed calcium with no pH climb.

Other needs for calcium:
• Calcium is a vital component in blood clotting systems and also helps in wound healing.
• Calcium helps to control nerve transmission, and release of neurotransmitters.
• Calcium is an essential component in the production of enzymes and hormones that regulate digestion, energy, and fat metabolism.
• Calcium helps to transport ions (electrically charged particles) across the membrane.
• Calcium is essential for muscle contraction.
• Calcium assists in maintaining all cells and connective tissues in the body.

Other needs for Magnesium:
• Normal calcium balance in organs
• Healthy muscles
• Healthy nerve transduction
• Healthy calcium balance in blood vessels

About Plaster of Paris for calcium:

Plaster of Paris is often recommended as a source of calcium for ponds or aquariums in place of aragonite, Wonder Shells or similar, this is NOT a substitute for Wonder Shells aragonite or similar and is not the same!
Plaster of Paris is a poor choice for GH or Calcium as Calcium needs to be in the proper ratios with other elements such as Magnesium to be utilized by aquatic life (such as osmotic function).

For a further explanation of Plaster of Paris in aquariums and Ponds, please read this article:


Electrolytes are molecular substances containing free ions which behave as an electrically conductive medium. In fish (or other living things) the primary ions of electrolytes are sodium (Na+), potassium (K+), calcium (Ca++), magnesium (Mg++), chloride (Cl-), phosphate (PO4---), and hydrogen carbonate (HCO3-).
Fish and other aquatic life forms such as shrimp require a subtle and complex electrolyte balance between the intracellular (inside the cell) and extra cellular (outside the cell such as plasma membranes) environment. In particular, the maintenance of precise osmotic gradients of electrolytes is important. These gradients affect and regulate the hydration of the fish, blood pH, and disease resistance and are important for proper nerve and muscle function.
Salt is commonly used in a dose of one tablespoon per 5 gallons (20 liters) in freshwater aquariums. This is one way to add some electrolytes, but this should not be the only (
Wonder Shells add many other electrolytes which is a reason I recommend these). Salt also will aid in disease prevention as it will help with the generation of the slime coat (or Mucous) on fish as salt acts on the osmotic gradient. But care needs to be given with salt sensitive fish such as catfish not to exceed this amount. Another aspect of salt is that although it aids in the prevention and even treatment of Freshwater Ich (Ichthyophthirius multifilis), it is poor treatment for a full blown infection despite many anecdotal comments by many.

For my FULL article about aquarium GH, electrolytes, Calcium, pH and much more, please follow this link: http://www.americanaquariumproducts.com/AquariumKH.html

Professional aquarium maintenance experience since 1978 as the owner of one of the larger aquarium maintenance companies in LA, CA.

I have been in the hobby since 1969.



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