1/8th of what full rpm amperage is in a given pool pump. This is the theoretical number. In actual practice I find 1/5th the power consumption for every time you half the motor rpm. The flow drops linear with rpm. So 1750 repm would be half flow and 1/5th power consumption of 3450
But what is the difference in flow rate? Is the purpose of having a pump to run water through the filter? So at half speed what is the flow rate compared to full speed? Don't you have to run your pump to get at least 2, preferably 3 complete filter cycles per day?
The relationship you are asking about are called "affinity" laws. Pump speed is proportional to water flow. Pump energy is related to the cube of the pump speed. So running the pump at half speed pumps half the flow rate but uses only 1/8 of the power. To pump the same amount of water at half the pump speed, you have to run the pump for twice as long, but you use 1/4 (1/8 + 1/8) the electricity.
There is a 1000L storage tank next to the pump. You can see it in some of the other videos on my channel like this one: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-dGxntivlQf0.html