1. Yes you will need to purchase dechlorinator, because aside from the chlorine, there are some other things in tap water that can harm the fish.

2. It's not too expensive. A large bottle is in the ballpark of $20USD, and will be more than adequate for your overwinter needs.

You just pour some in as you add water from the tap. Quite easy.

BTW why are you doing 50% water changes? That seems pretty excessive. Also make sure when you change your filter media you don't rinse it off in the tap water. The chlorine will kill your bacteria. Something different to consider going forward to city water from well water.

When I had my fish in the basement two winters ago, I just added water as evaporation occured and cleaned my bio filter every week. Limiting food intake certainly helped slow the buildup of waste.

Good luck.

I use a trailer dechlorinator filter most of the time, but if I choose not to, I, too, like to use a dechlorinator just to be safe. I know a couple of people who don't use anything, but they have bigger ponds than I do.

Groundbeef::

I do 50% change because there are 279 goldfish in one of the pools. I don't have that great of a filter in there pool..
If you have any good websites that I could use to buy the dechlorinator from, send them my way..Thanks Sheri

Oh my. That's a lot of fishies!

I've used these guys before. Here is the water treatment page:

http://www.webbsonline.com/catalog/treatments/index.html