TIL quenching in dirty water is why half your hammers keep cracking

I watched a guy at the NWBA meet in Longview plunge a fresh 1080 hammer head into a bucket of black, oily water that looked like it came out of a lawn mower, and he acted like that was normal. Dirty water changes how the vapor jacket forms around the steel, so you get uneven cooling and hairline cracks you don't see until the head lets go three months later. I know because I cracked four hammers in a row using my quench tank without changing the water, and every single break started in the same spot about an inch above the eye. Now I dump the tank after every two heads and scrub the scale off with a wire brush first. Anyone else running a dirty tank out of laziness, or am I the last one holding this bad habit together?