HTH Logo

hth® calcium hardness increaser, 4 lbs.

hth® calcium hardness increaser is used to raise the calcium hardness of swimming pool water. Low calcium hardness may cause the pool water to be corrosive, resulting in damage to pool surfaces and equipment. Plaster  finish pools may be etched or stained if the calcium hardness of the pool water is not properly adjusted. The calcium hardness of chlorinated pool water should be maintained in the range of 200-500 ppm.        

  • Raises calcium hardness levels
  • Prevents corrosion of metal & plaster surfaces
  • Compatible with salt systems
  • Apply directly to pool

Buy Now

Testing and Balancing

Test Your Water

How often you should test and balance your pool can vary based on how often you use it and a number of other variables, but it’s important to remember that, for chlorine and pH, you should usually test your pool two to three times a week. That may sound like a lot, but water balance is vital for your pool’s health and the health of the people who swim in it. When your pool is out of balance, your sanitizers can be less effective, the water can cause irritation to the skin and eyes, and if the water gets imbalanced enough, it can even damage the pool’s surfaces, structure, or equipment

Shock Weekly

In ideal circumstances, shocking your pool just once a week will keep it looking clean and clear, but any heavy rainfall, signs of algae, use by lots of swimmers, or periods of very sunny weather can deplete free chlorine levels, which means an extra dose of hth® shock is needed. Sundown is optimum time to shock your pool because the chlorine can work without fighting the sun's ultraviolet rays and has more time to restore water clarity.

hth® Test to Swim app

The hth® Test to Swim® water testing app is essential to spending more time splashing and less time guessing! Our mission is to simplify water testing by providing accurate and convenient water analysis treatment and recommendations in the palm of your hand. 


  • Easily input your water results
  • See immediate analysis of your water 
  • Get list of items needing immediate attention 
  • Step by step treatment recommendations and dosing instructions for balancing your pool 
  • Auto-save historical water test information for easy comparison 
  • Liquid testing option 
  • Build pool profile with pool size calculator 
  • Online retailer links for recommended products 
  • How-to videos on everything from basic pool maintenance to specific pool problems

Ratings & Reviews