Frothiness Causes

• Air in a swimming pool is one cause of frothy water. It can happen when there's an air leak in the pool's water return line. Another reason for frothy pool water is the oils and lotions from swimmers that invariably end up in a pool's water. The water can also suffer from low calcium hardness, meaning it's too soft. Soft pool water often froths up from agitation. Additionally, frothy swimming pool water can occur after you've treated the pool with an algaecide to kill off pool algae.
  
  

Preventing Frothiness

• Always check any swimming pool return lines for air leaks and then fix them to help prevent water frothiness. Swimming pool users should wear only waterproof or water resistant sunblocks, lotions and oils if they intend to swim. The best preventative against frothy swimming pool water is to ensure your pool's water chemistry is in balance at all times, including its pH, total alkalinity and calcium hardness levels. A pool's pH should be between 7.4 and 7.6. Swimming pool total alkalinity levels should be at 80 to 100 ppm. Keep calcium hardness between 200 and 400 parts per million, or ppm, with a maximum of 1,000 ppm. Lastly, maintain swimming pool chlorine levels at 2 ppm.
  
  

Raising Hardness

• If you test your swimming pool's water and find that it's too soft due to low calcium hardness, you'll need to make the water harder by adding calcium chloride, which you can find in pool supply stores. Be careful to only add as much calcium chloride as is necessary to raise its calcium hardness. If your pool develops excess calcium hardness, the only solution is to drain and then refill it.
  
  

Adjusting Levels

• You can raise the pH in your swimming pool by adding sodium carbonate, about 1 lb. per 25,000 gallons. Lower pH by adding muriatic acid at 1 qt. in 25,000 gallons. Raise a swimming pool's total alkalinity by using sodium bicarbonate, at 3.5 lb. in 25,000 gallons for a 10 ppm increase. Lastly, lower total alkalinity with either muriatic acid or sodium bisulfate according to package instructions.