How to change water automatically in fish tank?

Drainage principle: Because the solenoid valve is closed at ordinary times, the tee is actually a two-way connection. Because the other end of the drain pipe is lower than the water level line, water will automatically flow out through the drain pipe. The drainage speed can be controlled by controlling the flow regulator of the infusion tube. When there is too much drainage, the float on the water level control switch sinks, causing the switch to turn on, the solenoid valve to open, and water is added. When water is added to a certain position, the float rises, causing the switch to close, stopping adding water and continuing to drain.