i base what i say on the common sense that taking any fish from one extreme to another is unhealthy. i suppose we cant be too careful with thinking nitrates are no different. we go out of the way to protect our little finned-friends 
now, we dont know for sure, but if he has a heavily stocked 55, and his nitrates go sky high in the times between a wc, then he adds clean water almost cutting levels in 1/2 if doing a 40% wc. thats cause for stress i would imagine.
also, i KNOW i had read along my travels on here that if you take a fish from horridly disgusting water, you need to gradually clean the water/tank and acclimate him to the lower levels and cleaner water, as to not shock their systems.
now, we dont know for sure, but if he has a heavily stocked 55, and his nitrates go sky high in the times between a wc, then he adds clean water almost cutting levels in 1/2 if doing a 40% wc. thats cause for stress i would imagine.
also, i KNOW i had read along my travels on here that if you take a fish from horridly disgusting water, you need to gradually clean the water/tank and acclimate him to the lower levels and cleaner water, as to not shock their systems.
