Thanks @Hamish_McGregor. Ultrasonic sensors are so versitile and fortunately i’ve had a bit of experiance with them. A few commercial products are available for just this use case, however none of them are less than $10 or ‘web enabled’.
They would be cheap enough to make but suffer from a few issues.
- dead band - this is to prevent unwanted reflection immediately infront of the sensor giving false distance readings. 2) unwanted reflections - water is often not flat (citation needed) and tank walls can mess with the reading too. 3) deployment - I would need to cut a hole in the top centre of my tanks to use it. Thats something I’m not able to do on all of my tanks.
Which is why I opted for my approach which was cheap, non invasive and revived an old and unfinished project