A Brief Analysis of Water Used in Daily Fishkeeping

In daily fishkeeping, there are generally two types of water: circulating water, which uses beneficial bacteria to control water quality, and green water, which uses algae to maintain water quality.

**Applicable Environments and Basic Conditions:**

**Circulating Water**: Suitable for indoor environments with low light and a power supply. A pump capable of completely draining the tank water within 15 minutes is required. During normal use, the pump should not be turned off for cleaning the filter for more than 1 hour. The pump's outlet should ideally be designed to disperse water like a rain shower. Additionally, a strong filter box is needed, along with filter media that can hold at least one-fifth of the tank's volume. It is recommended to use double-layer black coarse biochemical cotton as the first stage of filtration, with a large number of glass rings or ceramic rings as the main bacterial bed. At the end of the filtration process, a small amount of coarse coral sand and wheat meal can be added. The entire filtration system should be light-proof, and an electric heater should be prepared to maintain the water temperature between 25-30 degrees Celsius. With these conditions met, circulating water will be adequately prepared.

**Green Water**: Best suited for outdoor environments with strong natural light and good ventilation, where there is a water source and easy drainage. The conditions required are: the fish container should be shallow, controlled at 20-30 cm, and the water surface should be large enough; for two 10 cm fish, a minimum water surface diameter of 70 cm is required.

**Two Rules for Starting the Tank**: 

**Sparse stocking, no feeding**.

New water feeding → Water quality deteriorates rapidly → New fish suffer from rotting flesh, fins, and gills. This is an experience every fishkeeper has gone through. The fundamental reason lies in the fact that new water has little self-purification ability. (As a side note: similarly, circulating water that has been treated with sterilizing agents may also experience this issue due to a reduction in nitrifying bacteria. Green water has fewer problems in this regard, but algae can absorb medications, leading to reduced effectiveness. Therefore, it is advisable to use new water at the same temperature for medication baths.)

If, during the tank setup process, the water has a noticeable fishy or unpleasant odor, change 20% of the water immediately, or perform small daily water changes. This is to ensure the health of the fish during cycling. The signs of a mature circulating water nitrification system include: dirty filter media, clear water, and a fresh smell from the filter media (this process takes a long time, usually requiring 2 weeks to 1 month at temperatures above 25 degrees Celsius). The signs of mature green water include: the water becoming slightly cloudy and starting to turn green, with a fresh smell (this process is shorter, taking about 3-4 days under strong light).

Once the water is mature, you can start feeding gradually, increasing the amount over time. For beginners, it is not advisable to feed heavily; generally, feed 1-2 times a day, with an amount that can be consumed in about 3 minutes. Any excess food should be promptly removed. Once you have a good grasp of water quality, you can challenge the limits of feeding amounts.

**Water Quality Maintenance:**

Maintaining water quality in circulating water is relatively simple. When the pump's output significantly decreases, clean the biofilm from the inside of the outlet pipe, or check for debris inside the pump. If the filter media becomes clogged, rinse the filter media. If the glass rings have a fluffy biofilm on the surface, rinse them as well. It is important to note that circulating water relies primarily on biological filtration, so do not clean any filter media too thoroughly. The main goal is to ensure smooth water flow within the filter box, allowing the filter media (bacterial bed) to function effectively. If the water quality feels thick, it is necessary to change part of the water. If you are unsure about the thickness, it is recommended to change part of the water every two months, with a change amount of over 20%. After changing the water, you can refrain from feeding for 1-2 days, and once the water quality stabilizes, resume feeding.

**Green Water Maintenance**:

Maintaining green water is slightly more complex and involves a comprehensive approach. Feeding should be done in the morning, and every evening, the bottom should be siphoned and replaced with equal-temperature new water, with a change amount of about 20%. On sunny days with strong light, to ensure sufficient dissolved oxygen in the water, shading or partial shading may be necessary. Feeding amounts can be slightly larger. On cloudy or rainy days, feeding amounts should be reduced, and the water change volume in the evening should be increased to lighten the water color. When the bottom algae are thick, water should be drained, and the container should be scrubbed. After scrubbing, mix new water in a ratio of 9:1 with old water, and refrain from feeding for half a day before resuming.

**Comparing the Advantages and Disadvantages of Two Types of Water**:

**Advantages of Circulating Water**: Easy maintenance, allows for larger feeding amounts, and can support higher stocking densities. Even in small containers, fish grow relatively quickly under suitable temperatures.

**Disadvantages**: Higher electricity costs, fish may appear dull in color, and power outages can be very dangerous. Water quality changes quickly, and filtration efficiency decreases with lower temperatures. At around 20 degrees Celsius, feeding should be reduced, and below 10 degrees Celsius, it primarily relies on physical filtration.

**Advantages of Green Water**: Vibrant colors and well-proportioned fish. During daily water changes, you can closely observe the fish's condition.

**Disadvantages**: Higher water consumption and greater labor intensity.

**Finally, Discussing Sick Fish and Water**:

Injuries and infections on the fish's body or gills can lead to serious water quality pollution, significantly increasing the burden of water purification and creating a vicious cycle (wound contaminates water → water quality cannot be purified in time → dirty water reinfects the wound).

Therefore, when treating such fish diseases, it is essential to address water quality by changing water to reduce the level of contamination, and to stop feeding to eliminate external water quality burdens. By rinsing the filter media, restoring or increasing the pump's water flow, you can adjust the filtration state (or dilute the green water color and increase light exposure to provide ample growth space for algae) to ultimately achieve a self-healing effect.

When it is necessary to remove sick fish for prolonged medication baths, always use new water and as large a volume as possible. If conditions allow, add an air stone for oxygenation, and monitor changes in water quality, promptly changing water and adding medication as needed.