For a long time I was looking for an elegant solution to fill up the aquarium. Then it occurred to me that you could also measure the water level with an ultrasonic sensor. So I set about designing an appropriate holder for the aquarium, which holds both the sensor HC-SR04 above the edge of the pool and the refill smart. I also designed a suitable housing for the controller. Together this results in my own refill automat for the aquarium, which measures the water level contactless and thus can never get dirty or worn out. Watch my YouTube video where I explain in detail how it works: https://www.youtube.com/watch?v=XzypXW8UTb4 Have fun building :-)