You would need a way to know the fluid level. you could use a tilt switch with a float to tell Arduino the container is full. You may be able to find a submersible sensor that can detect the level of water. I think the easiest way to would be to measure the weight then do the math to figure out at what weight the volume is 10% by dividing the full weight by 10. Then get a component to measure the weight to connect to Arduino. For the LEDs you could use a strip of 10 WS2812b which are individually addressable. If you use a non segmented diffuser the colors would look blended together. A segmented diffuser would show the ten individual LEDs.