Jul 25 2010

Aquarium Water Chemistry

Freshwater Fish Tank Bacteria

Fish Tank Aquarium Water Chemistry

To maintain your fish tank aquarium and enjoy your fish keeping and ensure that your fish and plants thrive it’s a good idea to know something about water chemistry and how it applies to your hobby. You should have a good water test kit to help in keeping the tank in balance which should include the following tests.

Chlorine and chloramine


Ammonia – fish produce ammonia as a waste product. It is poisonous and a build up will harm the fish. During the cycling of a new fish tank bacteria are encouraged to grow that convert the ammonia, first to nitrites and then to much less harmful nitrates. Ideally ammonia level should always be zero.

Chlorine and chloramine – Chlorine is used as a tap water disinfectant and needs to be removed before adding tap water to the fish tank. Leaving a bucket of water for 2 days will allow chlorine to evaporate. Chloramine is used in some areas as a water disinfectant and cannot be removed this way. You will need to buy a water treatment chemical specially made for fish tanks to remove chloramine.

Copper – Copper is harmful to fish and invertebrates and can be present in tap water where it can enter the water you have older pipes. It is also present in many fish medications.

Nitrates – Nitrates are only harmful to the fish at high levels and are produced by the nitrifying bacteria from nitrites which are harmful at much lower levels. The only way to lower the nitrate levels to below the acceptable 20ppm in your fish tank is to do regular partial water changes.

Nitrites – are poisonous and are produced by bacteria from the ammonia excreted by fish. They are then converted to the less harmful nitrates. The nitrite levels in a well cycled fish tank should be zero.

pH – is a measure of the acidity of the water. A neutral solution will have a pH of 7, an acid solution less than 7, a basic solution more than 7. Although different fish prefer different pH levels most fish will be fine over a wide pH range. Some fish prefer a pH as high as 8.5, some as low as 5.5. Unless you have fish with these extreme requirements there is usually no need to adjust the pH of the water.

Phosphate – this chemical can be present in fish food, tap water or from decaying plant material. It is a fertiliser for plants and can cause an algae bloom if the levels are too high. Regular water changes should keep the phosphate at an acceptable level.

Salinity – the concentration of sodium chloride in the water is important if you have a salt water tank and can be measured using a hydrometer.

Hardness – dissolved minerals in the water contribute to the hardness. The main minerals present in tap water that cause hardness are magnesium and calcium and these will be present to a greater extent if you live in a hard water area. It is not really an issue for freshwater tanks unless you live in an area where the water is very soft. For saltwater tanks it is more important as some invertebrates and live corals need these minerals to grow.

Fishless Cycling for a Freshwater Aquarium

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