You could try using biocides. What's your process?
I wonder if UV illumination of the lichen would work to preferentially eliminate tiny animals. I think the algae is rather resistant when it is in the lichenized body.
Currently I am breaking up lichen into small pieces and placing the pieces into jars with sterilized water that contains some nutrients (ammonium sulfate, (di)ammonium phosphate, potassium sulfate). I place the jars through my apartment under different light conditions.
The idea is to preferentially grow algae by having low phosphate and exposing to the sun, dilute, grow again, dilute, and repeat a few times to purify. Similar to how I purify a wild mushroom through agar transfers. In the past I did succeed growing a bunch of Trebouxia but I left those jars standing for two years and now they have a wild mixture, so I am starting the process again.
Microscopy
Anything related to things that are too small to see them with the eye, and the tools used to observe them.
This space is quite general in scope - microscopes, microbiology, small component electronics, questions about buying optical components, etc.