<a href=showthread.php?s=&postid=9992906#post9992906 target=_blank>Originally posted</a> by titus164
i was under the impression if you change more than 20% over the span of a few days, will shock the fish. Either changing all at once or not, I heard making a massive water change in a short time frame can negatively impact the tank. Please correct me if i am wrong as i heard this from a credible source.