If it's only a few days it's not necessary. Adding just a pinch of fish food occationally will keep the bacteria going indefinately.

If you do a large waterchange with chlorinated water you will certainly thin out the bacteria population. It would be better to put the water in a seperate container and let the chlorine dissipate before you use it on the water change. Running it through GAC will also work and so will AmQuel although AmQuel is the least effective IMO.