Here are some of the basics of fish tank water chemistry you must know so that you’ll be able to test and treat the water if you see that fish are getting sick or are dying.Since water in an aquarium is not flowing anywhere like water streams in natural environments, it’s necessary to maintain the habitat just like you’ll see in nature so that fish feel “homely” and enjoy the habitat you have created for them.

It is necessary to learn these simple chemical characteristics of water because most of the times tap water is used to fill fish tanks which is not suitable for fish to survive and before you add fish the water must undergo changes through a biological process called as “Nitrogen Cycle“.

During this cycle, which varies anywhere in between 2 weeks to 2 months period, bacteria establish themselves in the water creating healthy environment for fish. Once this cycle is complete, here are the water components that need your attention.

1) pH Value – This is value determines how much acidic your tank water is. Normally this value varies from 0 to 14 where 0 is the most acidic water. For fish to survive in your tank it is necessary to maintain a pH value between 6.6 to 7.8. If after making pH tests you notice that it is lower or higher then you must add chemicals externally to create pH balance once again.

2) Ammonia – This gets created in all fish tanks because of solid waste produced by fish and uneaten food that rots down. The normal reading for ammonia in a healthy fish tank is 0 ppm (ppm = parts per million). Normally the bacteria in the fish tank that has completed the nitrogen cycle will bring the ammonia levels down but if you find that it is more than 0 then there are products available in the pet stores to maintain the ammonia levels too.

3) Nitrites – These are less harmful than ammonia and are formed by the bacteria that break down the ammonia in aquarium water. Like ammonia the nitrite levels must be maintained to 0 ppm. Normally a water replacement of 25% every week will take care of nitrites levels.

4) Nitrates – The bacteria break down ammonia which produces nitrites and when these bacteria further break down nitrites your tank will have nitrates in it’s water. Actually if you find presence of nitrates in your aquarium water then you can safely assume that the “Nitrogen Cycle” has completed. If after performing tests you find that levels of nitrates are more than 40 ppm then you’ll need to consider frequent water changes, but not the entire water.

5) General Hardness – This test measures the amount of dissolved calcium and magnesium in fish tank water. The correct amount of these dissolved minerals will help maintain pH value of your water. When these dissolved minerals are higher the water becomes hard and unsafe for fish. The general hardness of water is measured in dH and the acceptable value for most fish are 5 to 12 degrees. Some water testing kits measure general hardness as GH and its acceptable value of 150 ppm.

6) Carbonate Hardness – This test is necessary to maintain alkalinity of water and too less alkalinity will results in lot of changes too frequently in pH value of fish tank water. This can be harmful for fish health. The unit of measurement for this test is dKH and the acceptable value is 7 to 12 degrees. Some water testing kits refer to this as KH and the acceptable value is 80 to 300 ppm.
To perform these and more tests the recommended water testing kit is

(paidlink)

API Freshwater Master Test Kit

Essential Fish Tank Chemistry For Beginners