Conflict resolution for hash-backed unique constraint of large text bodies
I don't know why the results of a biochemical experiment would be enforced to be unique in the first place, but you can use an exclusion constraint that tests for equality.  It will automatically resolve hash collisions by doing the character-by-character comparison.
alter table foo add constraint foo__bar__un exclude using hash (bar with =);

But you should upgrade to something newer than 9.6.