As the ecosystem in nature is very fragile and prone to triggering severe consequences if the balance of elements is altered so is the ecosystem inside of an aquarium a very fragile thing, leading to devastating consequences if the balance is thrown off.
It is important that the elements of the water be tested on a regular basis and necessary alterations made as frequently as possible. There are many elements which are important for the well being of your aquarium fish; temperature and pH have the greatest immediate impact on their well being and should be monitored closely. There are certain precursors which can be tested in order to anticipate problems with these elements, and by closely monitoring these precursors an attentive owner can prevent the death of their fish in much the same way that an attentive physician may be able to head off the formation of cancer.
The carbonate hardness, or kh, level of the water should be monitored closely using one of the commercial systems which are available on the market. These can be purchased from any saltwater fish dealer or through an online retailer such as Amazon.com. The hardness of the water is significant because it can lead to rapid swings in pH. These swings can cause the fish to become stressed, making them more vulnerable to disease than they would be otherwise. This means that it will take very little to make them ill; the germs from the fingers of human hands could be enough to cause an epidemic and wipe out your entire aquarium population. Remember what smallpox did to the Indian populations because their immune systems were not prepared? The consequences could be just as fatal.
Fish will generally adapt to the hardness of the local water supply fairly quickly; however, to truly thrive their environment should be as close to that of their natural habitat (i.e. where they would be living if they were not living in a tank in your home) as possible. This is particularly necessary if you are entertaining the notion of breeding your fish-bear in mind that much like human newborns baby fish will not have had a chance to adapt to an environment that was not suited for them, and many may die because of this. Organic water plants will also thrive best in water that closely resembles their natural habitat. There are many commercial products available which will help to soften the water if the kh level is too high.
By carefully monitoring the kh levels of your aquarium you will be able to stay one step ahead of the elements and help to ensure that your fish have the best chance of survival possible.