It boils down to how your doviis eat.
If it eats like a pig, then 1" a month is reasonable
If it hardly eats at all, then maybe 1/2" every few months or even longer.
From my experience huge waterchanges did not help much on making my picky eater male dovii grow faster, but recently it has been eating like a pic and it seems to have grown overnight.
no matter wat it really comes down to the size of the tank..water quality and the foods..you it high quality frozen foods...like krill and beefheart...will make him or her grow at a fairly rapid rate...