People here say generally 1/2 to 1 inch per month for baby polys, and mine have followed that rule.
As for the kuhlis, it depends on the individual fish. My prior Palmas ate a few, yet my Delhezi (who was the same length, 6") did not.
ETA: my kuhlis are/were like 6 years old so they are huge for kuhlis.
mine have been growing 1-2" a month



