It's one thing to purchase chemicals on line (for price I'm assuming?) :-? but quite another to understand how to balance water. My suggestion would be to support someone local who understands water balance, offers free water analysis and will help you keep your water clean, clear and safe.
I've seen many people save a few bucks only to drain and refill twice as often due to poor water quality, not to mention having unsafe or even harmful conditions. Don't step over a dollar to pick up a dime...