What Causes Phosphates in Pools? How to Control Phosphates Level

What Causes Phosphates in Pools

Photo: aquamasterspool.com

Phosphates are ever-present in pools, but it’s not until the pool turns green that we get concerned because its likely that an algae bloom has struck.

Elevated levels of phosphates in your pool can cause a surge in algae growth, which can, in turn, make for a terrible swimming experience and a potential health hazard.

Here, you’ll discover more about phosphates and how to remove and even prevent their surge.

What are Phosphates?

Phosphates are organic compounds derived from phosphoric acid. The name is, in fact, representative of a class containing many types of phosphates.

These compounds are forms of the phosphorous element, and they occur naturally, making them very widespread and present in most biological systems on earth.

Also, they serve a critical role in organism growth, especially plants, a characteristic that makes them common in many industrial and agricultural applications.

What Causes Phosphates in Pools?

What are Phosphates

Chemicals and Runoff: There are many possible sources of phosphates in your pool. Landscape fertilizers, which have high phosphate content, for instance, can be blown into the pool by the wind.

Organic Elements: Leaves, soil, twigs, mulch, and algae, all of which have relatively easy access to the pool, also contain phosphates which can lead to an increase in the concentration of the same in pools.

Swimmers: Often, swimmers will introduce many compounds in the pool including skin and hair products, oils, sweat, and even detergents that may be present in towels or bathing suits.

Over time, and especially in busy pools, these elements may hasten the buildup of phosphates to unconducive levels.

Actual Pool Water: Even without any foreign contaminants, your pool water may contain phosphates, which may have been added by some authority to reduce copper and lead levels, for instance.

It’s also common for some pool cleaners and chemicals stabilizes, stain, and scale removers, to contain phosphates even though in low amounts.

Should I get Rid of Phosphates?

Control, yes, but not getting rid of them entirely. Phosphates are typically present in your pool at any given time, but elevated levels of the same can promote the growth of invasive algae.

Even though many other factors can accelerate the growth of algae in your pool, some studies have established that phosphates can trigger algae blooms.

Read More: How to Get Rid of Algae in Pool

But phosphates hasten algae growth only when in high quantities. Therefore, the best way to determine if you need to contain the phosphates in your pool is by testing for the compound.

Since the maximum level of phosphate in your pool should be 100 ppb (parts per billion), if the test reveals higher levels, then that’s your cue to act and reduce it.  

How to Lower Phosphates in Your Pool

How to Lower Phosphates in Your Pool

Photo: orendatech.com

Apply Phosphate Removers (sparingly): The use of phosphate removers in pools is highly contentious because they can pose health risks if not used well.

These chemicals use a rare earth metal called lanthanum to bind to phosphates and remove them instantly.

The best practice when using phosphate removers is to consult a professional who is familiar with these chemicals and their application to pools.

Adding calcium: The addition of calcium to maintain the ideal levels of this compound (200-400 ppm) in your pool can help lower phosphates’ concentration.

Calcium, which is a positive ion, will bind with the phosphate, reducing the latter’s availability to algae, and consequently lowering it.

Control the use of pool chemicals: Excessive application of chemicals in pools can trigger imbalances in chlorine, alkalinity, and even pH levels of your pool’s water.

By using pool testing kits, you can constantly monitor the levels of these elements and then take action depending on the outcome. The goal is to use chemical in limited amounts, to keep phosphate levels constantly low.

How to Control Phosphate Levels in a Pool

How to Control Phosphate Levels in a Pool

Photo: swimmingpool.com

Skimming: You can keep your pool debris-free by regularly skimming out leaves and other common plant life occurring within it.

Pool brushing: Another common countermeasure that you can apply weekly to eliminate spores and buildup that tends mostly affects pool surfaces.

Read More: The Best Pool Brushes

Cover the pool when not in use: If you won’t be using your pool for extended periods, it’s best to keep it covered. Covering prevents elements such as debris and leaves from accessing the pool.

Read More: The Best Pool Covers

Contain algae using algaecide: You can control phosphate levels in your pool by focusing directly on the heart of the problem, which is algae.

By using a good algaecide, you can contain pool algae and keep phosphate levels in check. Make this a regular practice for consistent results.

Control calcium levels: Since calcium is a positive ion, it has a high binding affinity for phosphorous, a negative ion.

While phosphates are capable of softening pool water, low calcium levels can also elevate the concentration of phosphates.

Therefore, balancing calcium levels in your pool will naturally control phosphate concentration so that it is constantly within the ideal limits.

Read More: How to Remove Calcium Scale from Pool


Phosphates are constant in swimming pools, and while this is not a cause for alarm, trouble begins when they occur in excess.

Often, excess phosphates are caused by many factors including chemical runoffs, organic compounds, and human swimmers.

By maintaining the right chemical balance, adding calcium, and undertaking regular pool maintenance, you can contain the growth of phosphates.