To keep the population of guppies increasing, there are a few things you can do:
1. Provide a suitable environment: Guppies require a clean and well-maintained aquarium with the proper water conditions, including temperature, pH, and hardness. Providing a healthy environment will help ensure the guppies are comfortable and able to thrive, which can lead to increased reproduction.
2. Feed them well: Guppies need a balanced diet that includes high-quality commercial fish food, as well as live or frozen foods, such as brine shrimp, daphnia, and bloodworms. Providing a varied diet will help ensure the guppies are getting all the nutrients they need to stay healthy and reproduce.
3. Maintain a proper sex ratio: To keep the population increasing, it's important to maintain a proper sex ratio in the aquarium. For example, if you have too few females, the males may harass them too much, which can lead to stress and reduced reproduction. A good rule of thumb is to have at least two females for every male.
4. Avoid overstocking: Overstocking the aquarium can lead to overcrowding, which can cause stress, aggression, and reduced reproduction. It's important to provide enough space for the guppies to swim freely and establish their territories.
5. Control the breeding rate: Guppies have a high reproductive rate, and if left unchecked, they can quickly overpopulate an aquarium. To control the breeding rate, you can separate males and females, or use a breeding trap to isolate pregnant females until they give birth.