Ph Alert Lasts Up To 4X As Long As Competing Products. Ph Alert Is Also Almost Half The Size Of Competing Products. It'S Small, Clear, And Unobtrusive, So It Won'T Detract From The View Of Your Aquarium. Interpretation Simply Place Ph Alert Visibly Anywhere In The Aquarium Or Filter And Match The Sensor Color To The Corresponding Ph Reading On The Color Wheel. It'S That Easy. No Chemicals Or Test Procedures Are Required. When First Put In Service, Response Time Will Be About 30 Minutes. Thereafter, Ph Shifts Will Register Within Ten Minutes. Care No Care Is Required Beyond Removing Algae With A Clean, Soft Material. Do Not Use Bleach, Soap, Detergents Or Hard Objects To Clean The Sensor. Some Dye Medications May Discolor The Sensor. For Maximum Sensitivity, The Unit Should Be Read Under Natural Daylight Or Daylight Simulating Light. Sensor Exhaustion Is Indicated By A Visible Fading Or Washing Out Of Sensor Color. Once Exhausted, It Is Time To Replace Ph Alert