In order for fish to thrive, water must be similar to that which could be found in their natural environment. Poor water quality can cause fish stress, illness and even loss. Most common water quality parameters are Ammonia, Nitrite, Nitrate, and pH. All may vary over time and all are invisible to the eye which is why it is important to test weekly. Testing aquarium water weekly will aid in keeping your most important water parameters within the proper range for your aquarium.