Moving My Newt to a Larger Tank - Questions About Water

So I bought a nice new 10 gallon tank for my newt, I had him a 2.65 for the last two weeks and thought he deserved a better home.

Anyway, after moving his plants, gravel and water over, his tank was barely one tenth full. So I need to add more water, to about half the height of the tank, so that his new filter will work. My question is, how slowly do I need to add new water? Typically when you do a water change your only supposed to change about one third of it; but in this case I have to basically quadruple his water. Should I add maybe a gallon per day or what? I don't want to shock him.


Also, I have a side question: when he was in his smaller tank I was using store bought spring water, but now since I'll need more water I was just going to treat tap water with chlorine/chloramine remover. However, the tap water in Edmonton is about pH 8.2; is this too high? I was told by people at the pet store where I bought the water treatment solution that pH adjuster wouldn't be practical since the water here apparently has a really high buffering capacity. What should I do? Will the treated tap water be OK?

EDIT: By the way, I have a chinese firebelly

If you fill up a five gallon bucket, treat the water, and then let it sit long enough to allow it to balance out to the same temp as the tank water then you can add as much as neccesary.