The Nitrogen Cycle:
The disruption of the nitrogen cycle in the aquarium is the fastest common mistake to kill all your beloved goldfish. The reason the nitrogen cycle is so important is the aerobic bacteria that convert the toxic metabolic waste (ammonia) to nitrate which is less harmful to the fish.
Ammonia is a very toxic that it can burn the gills, fins, and body of a goldfish. It may break down the circulatory system and cause internal damage to vital organs. Ammonia is given off by goldfish, decaying food and organic wastes in large amounts.
Different type of goldfish has different tolerance to ammonia. Some can withstand high levels and some don't. Luckily, ammonia can be changed fairly quickly by a well running biological filter. The bacteria in the filter uses oxygen from the water to oxidize ammonia into nitrites, in which goldfish can withstand in low levels. Nitrites in moderate to high levels do cause a problem known as brown blood. This condition interferes with the oxygen carrying capacity of the blood. If high levels of nitrites are present, the fish can be seen near the surface or corners, breathing heavily. Salt will temporarily counteract high nitrite levels. If you feel you have this problem, add one or two tablespoons of salt to five gallons of water will help until you can find a way to reduce the nitrite level in the aquarium.
Nitrites are usually a problem when breaking in a new biological filter, as the bacteria that convert nitrites to nitrates lag behind those that change ammonia into nitrites. With a well-conditioned biological filter, the nitrites conversion to nitrate is quite rapid. Nitrates in low to moderate levels are rather safe for larger fish but is a problem for the fries as it will cause stunting and weakening of the immune system. Fortunately, nitrates are easily controlled by frequent partial water changes of 15% to 30% a week. Nitrates are also absorbed by plants and algae in the presence of light.
Cleaning The Inside Of The Tank:
Understand that the aquarium is a home for hundreds of different minute life forms, and that these billions of lesser life forms help to maintain the biological balance and good water quality of an aquarium, it is best we pay attention to how we clean the tank and not killing these beneficial life forms. The following is a few tips; (1) don't clean the filter element and water changes at the same time. (2) Cleaning the gravel over an under-gravel filter should be done regularly, but not over cleaned, as this is your major biological filter that keeps ammonia and nitrites in check. (3) Frequent partial water changes in order not to disturb the biological balance of your aquarium.
Think of your aquarium as a living colony of organisms; try to maintain as many of them as possible when you clean your aquarium. In doing this you will probably never have an ammonia or water-quality problem.eaning the Outside of the Aquarium:
With time the outside of the aquarium may have mineral deposits. Normally the deposit can be removed simply with clean cloth and water. To remove stubborn deposit, try using white vinegar. The acid in the vinegar is very effective in removing the mineral deposits and is harmless to the fish in small amount. Never use any commercial glass cleaner.
Most local city water is treated with chlorine or chloramine to make them safe to drink. If your water quality is good and the chlorine level is light, small water changes can be added directly to the tank without the need to neutralize the water. For larger water change, treat water with commercial chlorine and chloramine remover before adding water to the tank.