This is not mine bug. It has been mentioned by SkyeStorme in his Thermal Upgrade Part 17 video.
Algea terrarium is fed 1kg per task by dupes. Similar bug to Slime Machine which has been spotted before.
Workaround: Terrariums can be fed by automated system with liquid vent or submerged in water (it ain't bug, just tutorial! )
As stated in description.