I have lived in areas like that as well, though it is not an issue currently. But as long as you only change 10-50%, you should be fine. When I used to work in a pet store with over 100 aquariums, we did 50% water changes every week, using water straight out of the hose. Imagine the cost of using chemicals for that many tanks... At any rate, if it makes you feel better, then do it. It certainly can't hurt the fish. But if you want to save some money, use plain salt (not table salt, obviously). You can get it at your local grocery store, and a teaspoon treats 5 gals (or thereabouts), plus softens the water to ease the shock to the fish. Much better than the liquid chemicals, IMHO.