This is a dosing tube holder for use in reef/marine and freshwater tanks with 8mm (5/16-inch) glass walls. The dosing rack has slots four up to four dosing lines, plus an extra slot for an ATO line (probably works best with the Tunze Osmolator line of automatic top offs). The dosing rack also has a post that can be used to secure media bags.
The dosing lines I'm using are 5mm OD (specifically the RedSea dosing lines).
Note: this is remix of pw98's rack (https://www.thingiverse.com/thing:4397751)
The author hasn't provided the model origin yet.