Phosphates & Nitrogen are 2 naturally occurring elements in nature.  Phosphorous is a mineral & nitrogen is a gas.  In nature, they don't cause or contribute to pool problems.  However when they are "added" to the pool water, problems can arise -- especially in a poorly maintained situation.  The two most significant problems are moderate to severe algae blooms and chlorine demand.  Both elements are essentially set up as a buffet table for any algae to just come, eat & thrive.

Phosphates typically come into the pool from lawn care products; fertilizers, sprays, etc.  Phosphates can also come from dead skin cells! (Therefore, another good reason to shower before entering the pool.) These lawn care products can be brought in from people walking on freshly treated areas where they are literally walked into the pool.  They can also "drift" in when sprayed or just due to a windy day.  Remember, phosphates can come from your yard, your neighbor's yard or even from someone you don't even know who lives 3 blocks away.

One more thing about Phosphates in general.  They are essentially a NON-ISSUE.  Here's why...Phosphates are everywhere.  In fact many of the chemicals used to treat other problems such as metals are phosphates.  Phosphates have become a scape-goat for people who choose to not follow a good pool care program that includes proper water balance, solid levels of sanitizer, regular weekly additions of algicide and weekly shock treatments to oxidize organic waste.

Nitrogen can also come into your pool from lawn care products, but more typical, it's a case of sweat (shower before using the pool), urine (use the facilities before going into the pool) or other types of ammonia (ammonia is comprised of Nitrogen & Hydrogen - NH4).  If your local water supplier is using chloramines to sanitize the water, then large amounts of ammonia & therefore nitrogen are getting into the water.  Algae loves both nitrogen AND phosphates (phosphorous).

Here's the typical scenario with Nitrogen.  Nitrogen enters the water & combines with oxygen to form Nitrites (NO2).  The nitrogen will typically take the oxygen from the HOCl (hypochlorous acid - the form of chlorine that kills bacteria & algae) thereby causing a Chlorine Demand. You will have a difficult time maintaining chlorine, algae will thrive, the water will become cloudy, etc.  Once the nitrites have taken on more oxygen & become Nitrates (NO3), they are there to stay.  The only way to remove Nitrates from the water is to drain & refill with fresh water that is hopefully not contaminated with Nitrites.  Shocking & oxidizing will help to a certain degree.  Nitrates (NO3) you can live with, Nitrites (NO or NO2) are the problem causers.

With either Phosphates, Nitrites or Nitrates present, as long as a good, solid chlorine or bromine level is maintained, there normally isn't a problem.  However, when the chlorine is stressed out due to high bather loads, parties, rainstorms, etc. or if there is an existing chlorine demand problem, phosphates & nitrates just feed right into any algae present & the problem worsens significantly.

Treating the problem:

1.  Maintain good water balance - pH 7.4 - 7.6, total alkalinity 125 - 150 ppm, calcium hardness 200 - 250 ppm.
2.  Maintain a good chlorine or bromine residual in the water.
3.  Shock the pool (BioGuard® Burn Out Extreme®, Smart Shock® & Oxysheen® -- especially with bromine--are good products) & add algicide (BioGuard® Back Up®, Algae All 60®) weekly.
4.  Have a chlorine demand test done twice per season.
5.  Make sure swimmers & bathers shower before using the pool.
6.  If you know or suspect phosphates  have been introduced into the pool, PhosFree® from Natural Chemistry® is a great product that will remove the phosphates from the pool water, thereby depriving the algae of one of it's significant food sources.

To Make Your Chlorine Experience Fantastic, add Optimizer Plus® to create a level of 30 ppm to 50 ppm.  Using Optimizer® Plus will significantly reduce your Smart Stick® consumption and provide the wonderful, soft feel that is associated with biguanide treated pools.