Planted Tank Guru
Join Date: Jul 2010
Location: British Columbia, Canada
Water temp swings of up to 4-5 degrees F, up or down during water changes, should not produce any significant discomfort for most fish species, and is therefore of little concern.
Having said that, there's really no problem ensuring mixed hot/cold tap water for wcs to be within around 1 or 2 degrees F from tank water.