Pool Phosphate & Nitrate Problems

As a follow-up to my post below on Algae Eradication, it seems that I only briefly touched on a very important cause of algae – Phosphates.

Our discussion today focuses on the causes and effects of phosphate on a recurrent pool algae problem.

Phosphates are the number one cause of persistent algae problems. It is estimated that nearly all outdoor pools have measurable phosphate levels.

What are Phosphates?

Phosphates are compounds of phosphorous, a fairly common element on earth. Phosphates are naturally occurring in plants and rocks, and are also found in human and animal waste. They are a primary component in fertilizers and industrial cleaning products.

nitrates in pools

Phosphates were pretty big news in the seventies, when environmental groups began battling big industry against the practice of dumping waste water high in phosphates and nitrates into local watersheds. This was creating something called eutrophication. This is a process where bodies of water receive excessive nutrients that stimulate plant growth. Lakes and rivers were becoming overgrown with algae and plants, which dramatically affects the water chemistry, and ability for fish and other aquatic life to survive.

In swimming pools, our main goal is to keep eutrophication to a minimum. We don’t want to see any plant life growing – unless you are operating a “natural pool”, so it makes sense to keep levels of Phosphates and Nitrates to a minimum in swimming pools.

Phosphates and Nitrogen (the source of Nitrates) occur naturally, and they are all around us. Phosphorous occurs as a mineral and Nitrogen is a gas. Outside of the pool, they pose no problem, but once in the pool water, these two elements create conditions that increase chlorine demand to fight against microscopic plant life that uses both elements as a food source.

phosphate-chart-for-pools

How Much is Too Much? Phosphates enter the pool from many sources, so many in fact that a goal of zero pool phosphates may be unattainable. For swimming pools, 100 ppb, or 0.1 ppm could be considered an acceptable minimum, with levels over 300 ppb being treated with phosphate remover.

What Are PHOSPHATES and How did they get into my Pool?

Phosphates (PO4) are generally referred to as pollutants, although many sources of Phosphate occur naturally. We most often think of phosphates as what is used to give our laundry detergent its sudsiness. Phosphates are in cleaning supplies, fertilizers, some beverages, and even in some pool chemicals. You can’t see, smell or taste phosphates in your pool water, but it can be tested for, with a Phosphate test kit.

Phosphates commonly enter pools through wind blown fertilizer. If you have a lawn care service treating your beautiful yard, or if you fertilize azaleas surrounding the pool, it can be difficult to keep fertilizer from reaching the pool, via wind or water. Phosphates can also be left behind in our swim trunks, after removing them from the washing machine. Soaps, Shampoo and cosmetics all contain phosphates.

Phosphates usually enter a pool in the form of Tri-Sodium Phosphate, or TSP. During shocking of the pool, or adding of enzymes, TSP is broken down into the tastiest algae food known – Ortho-Phosphate. In this free state, ortho-phosphate provides all types of algae with a good food source.

What Are NITRATES and How did they get into my Pool?

Nitrates and Nitrites are products of Nitrogen gas. Nitrate, which consists of a single nitrogen atom connected to three oxygen atoms (NO3), is extremely stable or hard to remove. Nitrogen (NO) can enter your pool water from a variety of sources. It combines with oxygen to form a Nitrite (NO2). This extra oxygen atom is not just free floating around the pool (unless you are using an ozonator), so the agressive Nitrogen Oxide will steal another O atom from our chlorine molecule, HOCl. This makes our chlorine less effective and increases your chlorine demand. This continues as Nitrites take on another oxygen atom to become Nitrates, (NO3).

Nitrates have many of the same sources as Phosphates. Lawn care products, Acid Rain, Perspiration and Urine or other types of Ammonia (NH4). One study done in Miami found a higher incidence of Nitrates in community pools and pools which allow children, and lower levels in adult only pools. Nitrates cannot be removed from a pool except by dilution. AskAlan suggests draining 20% and refilling, repeatedly, until Nitrate has been lowered to manageable levels. You can test your pool for Nitrate levels, using a test strip for Nitrates.

How do I know if I have a Phosphate or Nitrate Problem in my Pool?

algae molecule

The first clue to you, may be that persistent algae that keeps coming back. If you have “tried everything” and the algae keeps returning, you probably have some amount of Phosphate or Nitrate contamination. If suspected, you can use the test strips to determine the level present in the water. Your local pool store may be able to test for this, or alternatively, perform a Chlorine Demand test, which can be an indication of a Phosphate or Nitrate presence in high concentrations.

Testing for Pool Phosphates

aquachek-phosphate-test-kit

Phosphates are tested with the use of a color comparison test. Powder packets are added to a small vial of water (Aquachek, Taylor) or phosphate test strips (Hach, Lamotte) can also be used. Results are ready within 1 minute, at which point the color of the vial solution or the test strip is compared to a blue gradient chart.

Phosphate test kits primarily measure orthophosphates. A Total Phosphate test kit will also measure for metaphosphates. This is quite similar to how Free and Combined Chlorine levels add up to Total Chlorine.

Removing Pool Phosphates

phos-free-for-pools

Fortunately, the process for removing phosphates can be accomplished fairly easily. The first step is to check and balance the water chemistry, kill any visible algae and have a clean pool filter at the ready.

Pour PhosFree into the skimmer, to form a phosphate trapping layer inside of your pool filter. After 48 hours, backwash the filter and retest phosphate levels to be sure they are below 100 ppb.

pool-perfect-plus-phos-feee

Also available from Natural Chemistry is another Lanthanum based phosphate remover, combined with a natural enzyme in Pool Perfect + PhosFree. Use for controlling phosphate levels, with a regular ongoing maintenance dose.

If you find over time that your phosphate level rises again, you may investigate some causes such as fertilizer or mulch washing into the pool during heavy rainstorms, over-hanging trees or dust storms.

Phosphates are the number one cause of persistent algae problems, and it deserved this additional column space.

If you have recurrent algae problems, I can almost guarantee that you have high levels of phosphates in your pool water. But don’t take my word for it, test for phosphates and find out for yourself!