AquaChek Biguanide 3-in-1 Test Strip. Tests for Biguanide, Total Alkalinity and pH. 25 strips per bottle. Biguanide is a chlorine-free sanitizer such as AquaSilk, Baquacil Chlorine-Free Swimming Pool Sanitizer and Algistat, BaquaSpa Sanitizer, SoftSwim Bactericide, PolyClearr MaxiPolish Swimming Pool Sanitizer and Algistat, or Revacil Swimming Pool Sanitizer. AquaChek Blue is a simple-to-use two-part test: Step 1 dip the strip and check the Total Alkalinity and pH. Step 2 re-dip the strip, moving it back and forth underwater for 30 seconds, to test the Biguanide level. To keep your pool or spa water at its best, test at least once a week, and write down results so you can track changes over time. Comes with complete instructions.