* Lack of oxygen: Unfiltered water accumulates waste products from fish, such as ammonia, nitrite, and nitrate. These substances are toxic and can deplete the oxygen in the water, making it difficult for fish to breathe.
* Accumulation of harmful substances: Besides waste products, unfiltered water can also accumulate bacteria, parasites, and other harmful organisms that can make fish sick.
* pH fluctuations: Without a filter, the pH of the water can fluctuate dramatically, becoming too acidic or too alkaline for fish to survive.
* Increased turbidity: Unfiltered water can become cloudy and murky, reducing visibility and making it difficult for fish to find food and avoid predators.
* Algal blooms: Without proper filtration, algae can quickly multiply, blocking sunlight and consuming oxygen.
In short, unfiltered water creates a toxic and unstable environment that is unsuitable for fish to live in.
Here's an analogy: Imagine you are living in a small, closed room with no ventilation. Over time, the air would become filled with your own breath, sweat, and other waste products, making it increasingly difficult to breathe and potentially causing you to become sick. This is similar to the situation fish face in unfiltered water.