Routine water changes are a vital part of maintain a balanced, healthy environment in any pond or aquarium. However, there is more to performing water changes than just dumping out the old water and adding in the new. In this article we wil discuss why water changes are important and how to perform them properly to insure a healthy home aquatic ecosystem. 

Why do we need to perform water changes?

While filtration systems can go a long way in maintaining water quality in ponds and aquariums, they have their limitations. Filters can remove macroscopic particles from the water, leftover food, fish waste, and can even help control toxic chemicals such as ammonia and nitrite. Filters do not address the slow accumulation of dissolved minerals, silicates, phosphage, or heavy metals in tank water that occurs through evaporation and subsequent replacement ("topping off") with new water. Dissolved mineral build up can cause your Total Hardness (GH) to slowly climb in a freshwater system. For many species of fish this can cause problems with their immune systems over time, making them more susceptible to illness. Phosphate and silicates will also slowly accumulate over time, both which will contribute to algae blooms and negatively impact both plant and coral growth. Most filtration systems do not address the slow accumulation of nitrate that occurs through the nitrogen cycle. Nitrate is safe at lower levels, but as it rises so does its impact on fish health. Address all these issues by actively removing water from the system and replacing it with new water

Removing things from the system is not the only reason to change your water. Over time vital minerals and electrolytes in your water are used up by your aquarium inhabitants, such as iodine and stromium. These trace elements are even more important if you have a tank that contains live corals or live plants. While you can dose these with supplements back into your system, refreshing the system with new water is also a vital part of maintaining these elements. 

Performing a water change

As a general rule of thumb you can safely remove and replace 20-30% of the water from the system daily. Removing anymore than this and you run the risk of the new water being too much of a shock to the system. In a bind you can change up to 50% of the water, but understand that this does carry more risk. Never do a 100% water change in an aquarium. Not only is this extremely stressful on the aquatic inhabitants in your tank, but it will start your tank back to square one and the nitrogen cycle will have to restablish itself all over again. If your system is experiencing a problem that requires more than the 30% it's better to do repeated changes every 24-48 hours than to change a larger volume at once. 

Before you remove water from your system make sure you have a source for enough new water to replace it. In order to prevent your fish from experiencing "shock, this water should be as close to your tank's ideal water chemistry as possible in pH, salinity, GH (freshwater only), and KH. replacement water should also be as close as possible to your system's temperature as well. All chlorine should be removed either by a filter or by way of adding a dechlorinator. It is a good idea to test your source water routinely to make sure you won't be inadvertantly adding things to your tank that may cause problems. Some water source may have high nitrates, phosphates, silicates, etc. that can negatively impact your fish and other aquatic life. 

Replacement water for saltwater and brackish aquariums should be preapred at least 24 hours prior to performing a water change in a large container where it can be continually mixed with a submersible pump or powerhead.  If your saltwater aquarium contains corals or other sensitive invertebrates you will want to use water that has been filtered with a reverse osmosis/deionization filter prior to mixing in your salt mix. Alternatively, saltwater can be purchased pre-made from many speciality aquarium stores.

Blackwater systems are special softwater systems which use peat moss to create water that is soft with a lower than neutral pH, more commonly used with Amazonian fish and discus. Blackwater water needs several days to be prepared in a separate holding tank with periodic testing until it has reached the right pH and GH levels. 

Once you are ready to start removing water from your system, check your filter and heater. Submiserible heaters will becomes extremely hot and can crack if left plugged in outside of the water. If when you remove water your heater will be exposed to the air, we recommend you unplug it. Filter pumps often do not handle running "dry" well either. If your filter's water inlet will become exposed as the water level drops it's best to unplug that as well.

The best way to remove water from most aquariumsis by way of a siphon. An aquarium siphon works by gravity and suction. Once suction causes water to start to flow down the tube it will continue as long as the inlet for the siphon remains both submerged in the water and the outlet remains lower than the top of the tank's water level. The inlet end of the siphon can be used like a vacuum to remove debris and particles from the substrate of the aquarium. Never use your mouth to start an aquarium siphon. Fish water can contain harmful bacteria that can make people very ill. Many newer siphons come with small hand pumps or have a one way valve in them to help start the flow of water safely. For ponds, you can remove water by way of a secondary pump, by backwashing your filter, or by way of a pond vacuum system. Otherwise the principle is the same as for an aquarium.

From there, refilling the aquarium is pretty straight forward. 

How often should you change your water?

As a general rule it's recommend you perform a water change at least once a month. However, you may need to change it more often depending on your tank's water chemistry readings and the stocking density of your fish. Performing a water test at least weekly will help you decide how frequently your system requires changing.