It's fine, just keep up the water changes and it should go back to normal. If you wish, you could try and mix some pH lowering agents into the fresh water before pouring it in the tank, but I do suggest not tampering with the pH too much. Goldfish are fine with it either way as long as it won't change very often, which it would, if you'd start mixing pH-lowering chemicals in there on a more regular basis.
Everything's a bit unstable in the tank while it cycles, so be prepared
