The importance of regular water changes in an angelfish tank, or any aquarium, cannot be understated. It is the most important maintenance performed to keep a healthy tank.
Fish cannot tolerate and adapt to living in bad water. Scalare angelfish are a little more tolerant, but altum angelfish need excellent water quality at all times. Freshwater scalare angelfish may be adaptable and might be able to survive in bad conditions, but they won’t spawn and they will have a shortened life span. Poor water quality will also inhibit the growth of an angelfish. If poor water quality exists in a tank and new freshwater tank fish are added, it’s likely the new arrivals will die. Therefore, it’s best to do a 20 to 25 percent water change about every two weeks. A large water change every two months isn’t as good as small, more frequent water changes. Larger water changes can also stress the fish, especially altum angels.
To change water, siphon water from the bottom of the tank into a bucket to remove some of the debris. A gravel siphon agitates the substrate and removes waste in the gravel and lets the gravel resettle. Some people use the wastewater as a natural fertilizer for potted and garden plants.
Adding Fresh Water
The water to replace the dirty water should be approximately the same temperature as tank water. If the water is a lot cooler, it could cause parasites and disease to attack the angelfish. Add a conditioner to neutralize chemicals the water department adds to purify the water.
Check the filters when doing water changes. Follow the maintenance instructions from the manufacturer. The filter media has beneficial bacteria, so don’t replace all the media at one time.
If the angelfish tank has an undergravel filter, don’t disturb the gravel. This will disrupt bacteria growth that breaks ammonia down into nitrates. The best undergravel filters have large tubes to pull the water upward. Put a siphon hose down them and siphon the waste that accumulates in the space between the filter and tank bottom. This is waste pulled through the gravel.