Why is the water in my turtle tank turning green?
Green water in turtle tanks is often the result of algae, which themselves are not particularly harmful. However, it’s important to check for conditions in your tank that could lead to algal overgrowth, as they could indicate other potentially harmful issues. Whenever you have a water problem (cloudy or smelly water, or high levels of ammonia or nitrates), the first thing to evaluate is your tank size and filtration method.
Conditions that promote algae
Algae tend to grow well in turtle tanks because the waste produced by the turtle serves as nutrients for the algae. First, make sure the turtles are in a large enough tank – a tank that’s too small will produce a highly concentrated waste that’s perfect for algae growth. As a general rule, the tank should hold at least 10 gallons of water per inch of turtle—the bigger the better. This means that an adult turtle will need a tank larger than 100 gallons. If the tank is too small, the water quality will be difficult to maintain and the turtle’s health and well-being will be at risk.
Find the right filter
The next step is to find a very powerful filter, preferably a canister filter with a rated capacity three to four times the size of the actual turtle tank. A pet store can help you choose one, as turtles are dirty and require extra filtering. Feeding turtles in separate containers also helps reduce the amount of waste in the water that can lead to algae growth. When cleaning the filter, do not sterilize it or use very hot water to clean it because you don’t want to kill the good bacteria in the filter. Good bacteria are needed to degrade turtle waste.
Make sure the lights on the turtle tank don’t stay on for too long. Leave the lights on for about 12 hours a day; if they’re longer, they may encourage algae growth (not to mention stress your turtle). Don’t try to reduce lighting too much – while light does help with algae growth, proper lighting (bastion and UVA/UVB) is critical to turtle health. However, if the tank is exposed to direct sunlight, it can be helpful to move it out of the light.
Keeping your tank clean is critical to water quality and helps algae grow – as the saying goes “dilution is the solution to pollution”. Keep in mind that there may always be some algae in the aquarium, possibly even on your turtle shell – trying to completely remove the algae is futile and unnecessary. The goal is to control algae, but more importantly, ensure good water quality.
You can also add animals that eat algae like snails and plecos. However, your turtle may eat them, so you have to keep replacing them.