My tank is solid blue with a transparent tube down the side so I can see how much water I have left,you can work out how much water you’re tank can carry by doing a quick calculation on the width and height of the tank once you have that figure say your tank is 500ltrs,if you were to measure the height and then divide that in to 5 each line you make is 100lts you don’t need a digital controller to do this.
I’m not knocking what you’ve done but you can do the same with a tape measure-calculator and pen.