One of the most important steps of swimming pool maintenance is water balance to keep the pool/spa water

SAFE. chlorine based tablet pool, pH needs to be correct. If pool water is not balanced correctly then chlorine sanitizer won't be working on killing germs and bacteria that can cause diarrhea/ear/skin infections.
COMFORTABLE. water balance needs to be correct or it will affect skin/eyes. pH should be neither too acidic nor basic in order to feel comfortable
CORROSION-FREE. imbalanced pool can be corrosive to the liner, ladders/hand rail and others like pump

CL2 can also get eaten up if lot of nitrogen (from debris, pee, sunscreen, sweat).It is best to test CL2 and pH levels all the time as they change daily depends on pool usage.

High alkaline water leads to high pH. Low alkaline water leads to low pH. Keeping your pH levels w/in proper range is important for keeping your equipment and pool finish intact. Your chlorine will dissolve quicker with low pH level. High pH levels make chlorine inactive.

This gives you useful info to adjust Chlorine and pH of your pool accordingly, if your tested results are beyond the recommended range below. A great tool that you might need for maintaining your pool water.

Features:

Essential tool for quick and accurate readings of ph & free chlorine as chlorine is the most commonly used disinfectant for water by killing bacteria, algae and microorganisms
Ideal for keeping your pool or spa within the safe Chlorine and PH ranges, no more chemicals or no more guess work
An electro-tester for testing pH and free chlorine (Cl2) levels in water for routine monitoring of pH and chlorine levels of swimming pools, spas and different water sources
Recommended Chlorine Level for pool and spa: 1.2 to 1.7ppm and 7.2 to 7.8ph for PH Level for pool and spa
Light weight and easy to carry, No chemical agent need and easy maintenance. Keep your pool/spa water safe, comfortable and corrosion-free.

Specifications:

Recommended level for pool and spa is 1.2 to 1.7ppm for chlorine and 7.2 to 7.8 for pH
Size: 190 x 120mm (main unit); 150mm long (probe w/ handle); 48mm long (probe only not including black band); 130mm long (cable only)
Power: 1 x AA 1.5V Alkaline Battery
Weight: 160g (battery excluded)

Set Includes:

1 x pH and Free Chlorine Tester with Probe
1 x English Instruction Manual