WATER QUALITY IN FRESHWATER FISH SYSTEMS

Jessie M. Sanders, DVM, CertAqV*
 
 Aquatic Veterinary Services
 4061B Soquel Dr
 Soquel, CA 95073
 cafishvet@gmail.com
 

Water quality is the most important aspect of fish health. Managing your water can be difficult for systems that are constantly turning over high volumes of fish, but should always be considered in management practices. Areas of water conservation may have increased difficulty with keeping good water at manageable prices. Taking steps to ensure good water quality can improve your fish health, longevity and yields.

The most important aspect of water quality is your nitrogen cycle. This cycle converts ammonia into nitrite, and finally nitrate. Ammonia is the primary waste product from fish, being excreted from the gills and gastrointestinal system. At high levels, ammonia is highly toxic to fish, as is its primary waste product, nitrite. Nitrate is the safest nitrogen compound and is used by plants and algae as a food source. However, even at high levels, nitrate can have the same toxicity as ammonia.

Nitrogen-fixing bacteria colonies will do the work of conversion for you; you just have to give them a place to live. Biological filters have many designs, but the most significant part is your biomedia, the structure on which your good bacteria can grow and thrive. This structure includes bio balls, mats, strapping, brushes, and essentially any porous surface with adequate water flow. These filters must be maintained regularly to ensure that old, dead bacteria are removed and water is able to easily flow through the filter.

pH and kH are essential in good fish health. Optimal pH will depend on your fish species. kH measures the buffering capacity of your water, also known as alkalinity. Your gH, or total hardness, will play a part in your kH. You need a sufficiently high kH in order to keep your pH stable. If your species can tolerate a wide range of pH, it is important that a stable pH is maintained. pH is based on a log 10 scale, so a pH change from 5.0 to 6.0 is a 10x decrease in the hydrogen ion concentration. The hydrogen ion concentration of your water can have a significant impact on many different biological processes in fish, most importantly those functioning in the gills.

Water parameters must be tested regularly and depending on your setup, may be required weekly, to daily to hourly. Choose a reliable test kit that multiple staff know how to use correctly. Additional testing may be required for new setups or possible contamination.