Archive for: January 2007

In addition to the hardness of water , the degree of acidity is also important for aquarium occupants. It is expressed in pH units , which reflect the amount of acid dissolved in the water relative to alkali. All natural water contains acids and alkali. If the water contains more acids than alkali , it is acidic ; if it contains more alkali than acids , it is alkaline. If the acids and alkali are equal , the water is chemically neutral. The pH scale ranges from 0 to 14.

Neutral water has a pH of 7.

Water with a pH under 7 is acidic ; the lower the pH , the greater the acidity of the water.

Water with a pH above 7 is alkaline. It becomes more alkaline as the pH increases.

Chemically pure water , such as distilled water , is neutral and has a pH value of 7 as long as it does not come in contact with the air. Carbon dioxide from the air dissolves in the water , forming carbonic acid and dropping the pH to about 5.3. Even water fresh from the ion exchanger has a low pH. With aeration , however , you can drive off the CO2 , and raise the pH.

Sharp pH variations harm the fish. Most tropical fish require pH values between 5.8 and 7. Only cichlids from the East African lakes need pH values between 7.5 and 8.5. For most fish the tolerable range of 1.2 pH units seems smaller than it really is , since a change of 1 pH unit indicates a tenfold increase or decrease in the degree of acidity.

You can measure the pH with pH indicators or electrical measuring devices.

 

Ammonia and ammonium are converted by filter bacteria ( nitrosomonas ) to highly poisonous nitrites , which in turn , are converted ( by nitrobacter bacteria ) to relatively non-poisonous nitrates. This ” bacteria nitrification ” requires a lot of oxygen.

There is a danger of oxygen deprivation …

When the oxygen concentration of the water is low , the bacteria work too slowly or not at all. The filter may then remain at the nitrite stage for too long , and the fish can perish from nitrite poisoning.

If the water contains large amounts of nitrates , the entire reaction can run in reverse. Thus nitrates are convertable to nitrites , which , in turn , are converted to ammonium and ammonia.

Nitrite poisoning has the same effect on fish as ammonia poisoning , lack of oxygen , or an excess of CO2. The fish dash around the tank , gasp for air near the surface , and suffocate if the water problem is not corrected. The nitrite content of the water should not rise above 0.2 mg per liter ; at concentration of over 0.5 mg many fish start gasping for air.

Fish tolerate nitrates better than nitrites. If possible the aquarium water should not contain more than 20 mg of nitrates per liter. Since tap water can contain up to 50 mg per liter , obviously the aquarium water will contain more than 20 mg per liter. Fish cannot tolerate more than 150 - 200 mg per liter.

What applies to ammonium and ammonia also applies to nitrates and nitrites. Change the water regularly and measure its nitrogen content in order to keep the nitrogen compounds to a minimum.

Swamp and land plants absorb nitrates. Even land plants can be put into the tank as nitrate consumers. Place the plant , like philodendron , close to the aquarium and let a few aerial roots grow inside the tank. They will soon branch out within the tank and absorb the nitrates.