Welcome to forum TBay,
looks like a nice secluded place.
before i drained it i would determine some basics first. if it were mine, i'd want to know how deep it is, if there is any structure to pond bottom, and estimate what kind of sludge build up there is if any. first thing i'd do is survey pond bottom from little boat. to survey my pond, i use a long telescoping measuring stick (mine is light fiberglass w/ measurements on it), you could also tape a mesuring tape to wood pole or something to that effect.
from there you might take a temp. profile. what feeds (water to) the pond? what kind of drain system does it have? does it get water all year round, would it be easy to refill? from your pic it doesnt look like it has excessive aquatic plants...are there any minnows, frogs, water bugs (i.e. is it supporting life other than catchable fish)?.....editing my post....i just remembered you said it had crawdads...that's great.
just a few of my thoughts.
i'll let others chime in on your need for chemistry.
