My Fish Tanks

Tropical freshwater aquarium fish reside in a wide range of water habitats– from fast-flowing mountain streams, to great lakes, to slow-moving rainforest rivers. Each of these biotopes, besides having unique fish species, has unique water properties due to environmental factors. Because fish do come from unique natural water sources, their water in captivity should have similar characteristics. To recreate natural settings, the aquariast should have some knowledge of basic water chemistry, specifically pH, water hardness, and the nitrogen cycle.

PH
The pH scale is a scale which is used to measure the acidity or alkalinity of a substance. The scale ranges from 0-14, with 0 being the most acidic, and 14 being the most alkaline. Water with a neutral pH of 7.0 has an equal ratio of H⁺ ions to OH^- ions. Water with a pH below 7.0, is considered acidic (having a more H⁺ ions than OH^- ions), while water with a pH above 7.0 is considered alkaline or basic (having a more OH^- ions than H⁺ ions). Almost all freshwater fish inhabit waters with a pH from 5.0-9.0, with the majority of these inhabiting water with a slightly acidic to neutral pH (6-7.5).

In aquaria, the pH of tap water can be manipulated though the use of phosphate, bicarbonate, and other buffers. However the pH may change despite these buffers. The development of a low pH can usually be attributed to decaying material such as plant and animal wastes. When the pH drops below 5.5, bacteria (Nitrosomonas) that break down ammonium are reduced, and the ammonium level rises.
Lowering the pH: The pH can be lowered by using a pH-lowering chemical (available at pet shops). Be aware that many pH-lowering products use phosphate-based chemicals. Phosphate is a nutrient that encourages algae growth. The pH can also be lowered by plants and fish during respiration, when CO₂ is exhaled into the water. In hard water, the pH may be difficult to lower. First, soften the water by peat filtration or reverse osmosis, and then try lowering the pH.
Raising the pH: The pH can be raised in an aquarium by adding baking soda (bicarbonate) or making a water change (thus removing some organic buildup which reduces pH).

Water Hardness

The degree of water hardness relates to the amount of dissolved minerals, especially calcium and magnesium, in the water. Water hardness is generally expressed in the amount of calcium carbonate (CaCO₃). Water hardness is measured in ppm (part per million), kH (carbonate hardness), and dH (degrees of hardness) or gH (general hardness). Water is expressed as soft (having few dissolved minerals) or “hard” (having many dissolved minerals. General levels of water hardness are expressed in the table below (1 dH is equivalent to about 17 ppm).

For most aquariasts water hardness is not particularly important. However, excessively soft water can cause problems. Because softer water has less buffering capacity due to a lack of CaCO₃ (a natural buffer), and is subject to pH crashes, where the pH falls dramatically causing harm to aquarium inhabitants.
Carbonate Hardness: Carbonate hardness (kH) is not used as a measurement of hardness as often. KH includes the presence of minerals and charged ions, other than Ca and Mg, dissolved in water.
Changing the Water Hardness: Water hardness can be manipulated in several ways. To make the water softer, the water can be filtered through peat moss or filtered through a reverse osmosis system. Ion exchange resins also can be used to lower the water hardness. Boiling water for a period of time can also reduce its hardness. To harden the water, filter the water through dolomite or crushed coral until the desired hardness is reached.
Electrical Conductivity: By running an electrical current through the water, the level of conductivity can be found. Conductivity indicates the amount of ions (electrically charged particles) are in the water. The higher the water hardness, the greater the conductivity. Testing the conductivity of the water only finds the total amount of ions present in the water, and does not give the origin of the ions, whether they are Mg, Ca, or Fe.

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