Planted Tank Guru
Join Date: Jul 2010
Location: British Columbia, Canada
There should be no problem with that, Drew.
But to be on the safe side, check the pH of the water out of your tap, and see how that compares to the usual range of pH in your tank.
If the difference is within 1.0, i.e. between say .01 and .09, that should be just fine.
If it's greater than 1.0, let the tap water gas off in the sink or a bucket for an hour or two, and then check it to see how it compares.
And don't worry about several degrees difference in temp between the tap water which has been left standing for a while, and that in your tank.
You're just doing percentage wcs - not complete changes of water, so there will be some equalization/dilution of both temp and pH when the tap water is added to the tank.