[jasno999]

I think you have no clue what you are talking about or doing. Just the way your are talking leads me to believe you don't even know the difference between a tank cycle and a water change. You are using the term interchangeably and you can't do that.

When you first get a tank you need to give it several week after you set it up to go thru a cycle. The basic principle is that you add a few fish or some fish food or a raw shrimp and get the filter running. It will take a few weeks but a biological filter will start to build up in the tank (on the filter and in the gravel) which will slowly break down the harmful chemicals in the tank such as ammonia and nitrites.

After the cycle is over that is when you can start adding fish to the tank. After that you are supposed to do partial water changes every two weeks or so. Timing of water changes and the % of water changed is all debatable but water changes are done for nutrient export not for cycling.

I have a feeling you set the tank up and simply thru the fish in and a proper cycle was never established. So I am guessing that the ammonia levels and nitrite levels are high in your tank and the fish are suffering and may die.

You should probably take the fish back to the store until you get your tank cycled. If you can't do that then I would do a 25% water change just about every 2 days for a while until the biological filter builds up. But in doing the frequent water changes you are going to extend the time it takes for that biological filter to build up. But you have no choice at this point.