Edit: I added a mirrored STL for anyone that has the indicator on the right side and not the left as I have.
To install this addon just print the original planter glue the floater to the indicator and press this addon behind the indicator as shown in the picture. This will keep this indicator upright and you will be able to monitor the water level.
It should be a tight fit and it should hold without any glue necessary but in case it can be glued with superglue.
The author remixed this model.