Delivering algae and water to an algea terrarium is a "Life support" errand, but emptying the storage of the polluted water is a "supply" errand. Therefore, the algea terrarium might stop working, even if it is fully supplied and all dupes have a high priority on "Life support". By changing the category of emptying the algae terrarium to "Life support", this can be changed.
Steps to Reproduce
1) Build an algea terrarium 2) Ensure enough water and algea is available 3) Mark disallow all jobs except "Life support" 4) Wait for the algea terrarium storage to run full of polluted water I expect the dupes to empty the storage of the algea terrarium, but nothing happens…
This issue has not been confirmed by a developer yet.