Amazon offers the API 5-in-1 Freshwater and Saltwater Aquarium Test Strips 25-Count Box for $5.84 with free shipping via the directions below. That's at least $3 under what you'd pay at a local store. These strips monitor levels of pH, nitrite, nitrate carbonate, and general water hardness. To get this deal:
  1. View the API 5-in-1 Freshwater and Saltwater Aquarium Test Strips 25ct for $9.30
  2. clip the $3 off coupon on the item page
  3. check out via Subscribe & Save for a final price of $5.84
Be sure to cancel Subscribe & Save once your order ships to avoid being billed for subsequent shipments.