Water Hardness and pH What it means for a tropical aquarium

What is Water hardness? Basically, it is the amount of dissolved minerals present in the water. Water hardness is of interest to aquarists for two reasons: to provide the proper environment for the fish. to help stabilize the pH in the aquarium. There are two types of water hardness: general hardness (GH) and carbonate hardness (KH).

General Hardness (GH) General hardness is primarily the measure of calcium (Ca++) and magnesium (Mg++) ions in the water. GH is commonly expressed in parts per million (ppm) of calcium carbonate (CaCO3), degrees hardness (dH) or, more properly, the molar concentration of CaCO3. One German degree hardness (dH) is 10 mg of calcium oxide (CaO) per liter. In the U.S., hardness is usually measured in ppm of CaCO3. A German dH is 17.8 ppm CaCO3.

General Hardness Parameters dH, ppm : very soft dH, ppm : soft dH, ppm : medium hard dH, ppm : fairly hard dH, ppm : hard higher : liquid rock (Lake Malawi and Los Angeles, CA)

What does this all mean for an aquarium? When a fish or plant is said to prefer "hard" or "soft" water, this is referring to GH. Incorrect GH will affect the transfer of nutrients and waste products through cell membranes and can affect egg fertility, proper functioning of internal organs such as kidneys and growth. Within reason, most fish and plants can successfully adapt to local GH conditions, although breeding may be impaired.

Carbonate Hardness (KH) is the measure of bicarbonate (HCO3-) and carbonate (CO3--) ions in the water. In freshwater aquariums of neutral pH, bicarbonate ions predominate and in saltwater aquariums, carbonate ions begin to play a role. Alkalinity is the measure of the total acid binding capacity (all the anions which can bind with free H+) but is comprised mostly of carbonate hardness in freshwater systems. Thus, in practical freshwater usage, the terms carbonate hardness, acid binding, acid buffering capacity and alkalinity are used interchangeably. In an aquarium, KH acts as a chemical buffering agent, helping to stabilize pH. KH is generally referred to in degrees hardness and is expressed in CaCO3 equivalents just like GH.

Buffering If you add a strong acid such as nitric acid to water, it completely dissociates into hydrogen ions (H+) and its "conjugate base" or "salt", NO3- or nitrate. The hydrogen ions freed in the reaction then increase the concentration of hydrogen ions and reduce the pH. Since nitric acid is the end product of the nitrogen cycle, this explains why aquarium pH tends to decrease and nitrates tend to increase over time. When the aquarium has some carbonate buffering in it, the bicarbonate ions will combine with the excess hydrogen ions to form carbonic acid (H2CO3) which then slowly breaks down into CO2 and water. Since the excess hydrogen ions are used in the reaction, the pH does not change very much. Over time, as the carbonate ions are used up, the buffering capacity will drop and larger pH changes will be noted. From this it is clear why aquariums with low KH seem unstable - as acid is produced by biological action, the KH is used up; when it is gone, the pH is free to drop rapidly as H+ ions are generated.

ADJUSTING FRESHWATER HARDNESS DOWNWARD If your local water is too hard for the fish and plants you desire, it can be softened. There are many ways to do this but some are more suited to aquarium use than others. The best (and most expensive, of course) is to use a reverse osmosis (RO) deionizer and mix the resulting water (GH=0) with tap water to get the desired GH. Peat moss can be used to soften and condition the water for use in South American cichlid tanks, but will add a slight tea color to the water. Peat filtering may be difficult to control. Peat should be boiled first to kill any unwanted organisms.

ADJUSTING FRESHWATER HARDNESS UPWARD If the local GH is too low, it can be raised by adding calcium sulfate and/or magnesium sulfate. This has the drawback of introducing sulfates (SO4--) into the water, so care should be exercised. Calcium carbonate can be used, but it will also raise the KH (this is ideal for the lucky few who have naturally soft water). Various combinations can be used to produce the desired results.

ADJUSTING CARBONATE HARDNESS Carbonate hardness can be reduced by boiling the water (inpractical for all but the smallest aquariums; let it cool before adding to the tank :-) or by peat filtering. Carbonate hardness can be easily increased by adding sodium bicarbonate. Calcium carbonate will increase both KH and GH in equal parts. One teaspoon (about 6 grams) of sodium bicarbonate (NaHCO3) per 50 liters of water will increase KH by 4 degrees and will not increase general hardness. Two teaspoons (about 4 grams) of calcium carbonate (CaCO3) per 50 liters of water will increase both KH and GH by 4 degrees. Different proportions of each can be used to get the correct KH/GH balance dictated by the fish and plants in the tank. Since it is difficult to accurately measure small quantities of dry chemicals at home, a test kit should be used to verify the actual KH and GH that is achieved.

What is pH? pH is a measure of the acidity or alkalinity of a substance. pH is measured on a scale of 1-14 with 7 being neutral. Something with a pH lower than 7 is acidic. Something with a pH higher than 7 is basic. Water has a pH of 7 naturally, but the water you are using in your tank will be different because of the chemicals that are suspended or dissolved in the water.tank These chemicals fall into three categories: acids, bases, and buffers. Acids are chemicals that lower the pH, or make the water more acidic. Bases are chemicals that raise the pH of the water, or make it more basic (or alkaline). Buffers are chemicals that can 'tie up' acids or bases and keep the water at a specific pH. Different buffers will keep the pH at different values.

What Can I Do to Change the pH Slowly and Safely? If you want to lower your pH safely, add a piece of wood to the tank as a decoration or add some peat to the filter system, but be aware that this will stain the water yellow or brown for a couple of years.decorationfilter system If you want to increase pH, add a sea shell or a coral skeleton. Remember, these will not give you immediate, overnight results, but they will introduce buffering agents to the water to help keep the pH more like you want it.

What is the water like out of the tap? How can we start with something different? Answer: Mimic Nature

What makes water “soft” in nature? Rainwater is slightly acidic (6.8) and VERY SOFT (0-4) since it has no dissolved minerals. Hence, it has no way of buffering, so it is extremely susceptible to pH swings.

What makes water hard in nature? Dissolved minerals from igneous rocks will raise the general hardness. Dissolved limestone will raise the carbonate hardness.

What makes water acidic? Tannic acid from organic material (i.e., leaves) lower the pH.

The Goal: To recreate your fish’s environment as closely as possible