THE IMPORTANCE OF CALCIUM, MAGNESIUM, AND KH IN YOUR AQUARIUM.
From this article: "CALCIUM, ELECTROLYTES, AND MAGNESIUM IN AQUARIUMS; How to maintain a Proper KH & PH, why calcium and electrolytes are important"

Many aquarists do not understand the need for calcium & magnesium and the effect of a proper KH (Carbonate hardness) in their freshwater aquarium.
Statements such: "calcium killed my fish" show this extreme lack of understanding of the basics of aquatic chemistry and how it acts on fish.

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 carbonate will absorb free H+ ions, and this causes alkalinity (which is the lack of H+ ions). To stop the 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 Calcium based products; Sea Chem Buffer (Marine OR Freshwater, Wonder Shells, or aragonite.
The Sea Chem Buffers 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 can be safely combined with Baking Soda as well.

If you have a very unstable KH level (drops rapidly), look into causes such as a large amount of decomposing organic material. The more organic break down (de-nitrification), the more acids produced. Some filters if not cleaned regularly can cause this; including canister, UGF, and Wet/Dry.

GH
General hardness (GH) refers to the dissolved concentration primarily of magnesium and calcium 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.

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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 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.

CALCIUM CARBONATE:
Calcium carbonate in your aquarium will keep a more stable Kh, 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. Besides helping to keep a stable Kh, 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 pH of a discus aquarium, 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

Be careful in the subject of calcium in aquariums, there is a lot of mis-information out there in the internet. Here is a gem of a bad answer I found on "Yahoo Answers" (not a trustworthy source of information)
QUESTION: What can I do to raise the dissolved calcium level in my living-reef aquarium?
ANSWER: Best Answer -Try adding bicarbonate of soda. Dissolve it first and add in small amounts taking regular readings to make sure that you are not adding too much.

WRONG!! -this answer is TOTALLY wrong! Sodium bicarbonate is the chemical compound with the formula NaHCO3. There is NO calcium in this formula (C stands for Carbon, Calcium is Ca) Wonder Shells, Calcium Polygluconate, even aragonite are better sources.


For even MORE ACCURATE information about KH, Calcium, and electrolytes please visit this site:
CALCIUM, KH, AND MAGNESIUM IN AQUARIUMS; How to maintain a Proper KH, why calcium and electrolytes are important.


It is noteworthy that a now banned Facebook Forum has also been using personal attacks on the findings of the article above, rather than actually read the article in full, read the citations, and realize that the author had done experiments to demonstrate his conclusions.

Here is the place to get Wonder shells:

*Aquarium Wonder Shells
Please note that this product is poorly named, as they are one of MANY tools to achieve a healthier aquarium, but are not a "Wonder" product that can make of for poor aquarium care or a poor set up.

REEF CALCIUM- For Marine Aquaria Reef Calcium is a concentrated (50,000 mg/L) bioavailable polygluconate complexed calcium intended to maintain calcium in the reef aquarium without altering ph.

KH and GH TEST KIT