In an old version of Grid2 (r720) from original mop there was a status that worked nicely for the Tortos encounter:

Would it be possible to enable this or is it not compatible with the current version of Grid2?

Alternatively increase the numbers for value based coloring to be able to be set to more than 200k. Max shield is 400k on Tortos.

You can try out 2.9.13-beta.
You can use the crystal-shell status in miscellaneous tab, or a standard debuff created in the debuffs section.