Ensure your water parameters are always correct for to the fish that you have. So an example is African cichlids. In this example, I am using the following parameters:

-25 degrees
-a pH of 8.4
-a KH up to 200 parts per million
-no ammonium
-as little nitrate and phosphate as possible

I am also adding a little bit of salt to the water to increase their immune system. Most freshwater fish will benefit from having a little bit of salt added to the water. The amount depends on the species of the fish, but 1 teaspoon per 10lt is normally right.

So you`ve gotten a bucket of water that you are ready to put in the fish tank for a water change. There are three things that need to go into this bucket, at a minimum: Number One is the water ager, Number Two is the salt, and Number Three is the carbonate (a kH powder). In Sydney tap water for example, there is no carbonate. Carbonate is an essential element, so it needs to be there. We get so many people coming down everyday with their fish dying and after testing their kH level, we find it is zero. Then we recommend them to put a little bit of carbonate hardness powder in the water and once they add the carbonate, their fish are fine. If you keep African cichlids and you use your cichlid salt, you don’t have to worry about adding kH powder, because carbonate is already in the salts that you use.

Make sure that you are adding carbonates to your tank if it is not in your water supply.

As per.com Paul Talbot
Taken from www.cichlidhub.com