Many people do not know why algae keep re-appearing in their swimming pool despite the use of shock treatments and superchlorination on a regular basis. Those folks may want to test their water for phosphates, a necessary ‘building block’ for algae blooms. Without phosphates algae has a really hard, if not impossible, time growing.
Phosphates can find their way into swimming pools in several different ways including, but not limited to, rainwater, water used to fill the pool, grass clippings and leaves that have fertilizer residue on them, poolside cleaners and chemicals, body fluids (which includes human waste — see “1 in 5 Americans Admits Peeing in Swimming Pools“), and vegetation (leaves, grass, etc.) which starts to break down in the water.
By removing phosphates with products such as Phos Free, a pool owner can greatly reduce their chances of having a bad outbreak of algae.
Won’t chlorine in the water keep algae from growing?
Tricky question because one would think that chlorine would stop algae from growing, but if other water parameters have strayed out of acceptable ranges or you have a whole lot of combined chlorine (instead of free chlorine) the chlorine in a swimming pool may not work as you’d hope — and the algae will grow.
We use algaecide so we don’t need to worry about algae, right?
Wrong. Most algaecides provide pool owners with an extra layer of protection against algae when chlorine levels drop too low but algaecides do NOT guarantee an algae-free swimming pool.
As an example, suppose your pool pump died over a long weekend when you and the family went camping and as a result no water passed through your automatic chlorinator for a few days. The algaecide in your pool water would slow the development and growth of algae blooms after all the chlorine got used up… hopefully long enough for you to return home, fix the pump, and get more chlorine back in the pool.
Moral of the story?
Frequent testing of your pool for critical water parameters such as free chlorine, pH, alkalinity and phosphates along with using of a good algaecide as a last line of defense makes sense if you want to keep algae out of your pool.