Reasons for use
Phosphate Removers should be looked at as an insurance policy NOT as a required part of pool care. If a user struggles to maintain the FC/CYA ratio then using a phosphate remover may help the user avoid an algae outbreak. Algae will occur if chlorine isn't added, but with a low phosphate level it will take longer to happen.
How do Phosphates help Algae Thrive?
Nitrogen (N), phosphorous (P) and carbon (C, mostly in the form of sugars) are all necessary for life. If any one of those elements are missing, life can not exist.
Micronutrients such as potassium (K), calcium (Ca), magnesium (Mg), iron (Fe) and others are all necessary too but in much smaller quantities. None of those elements can substitute for one another, they are all used in different ways and they are all required.
When water is deficient in nutrient sources, it is referred to as an “atrophic” condition - meaning it is missing nutrients. When water has too much of any nutrient in it, it is referred to as a “eutrophic” condition. Eutrophication of water leads to uncontrolled and unhealthy algae and bacterial blooms.
Pool water is eutrophic but it is also aseptic because of the chlorine sanitizer in it. So while properly chlorinated pool water will not have significant algae or bacterial growth, it is always susceptible to biofouling (unrestricted growth) because of its high nutrient content.
Reducing nutrient levels by either chemical removal (precipitation and filtration) or by water replacement will always help to reduce the incident rate and severity of biological growth.
Phosphate removal is simply one strategy for making water atrophic.
How to Test for Phosphates in Pool
When removing phosphates the goal is as low as possible. So it doesn't really matter how high they are to start with or where the test maxes out at. For the Taylor test there is a high limit version that goes up to 2000ppb but it's not necessary, just use water dilution if you max out to get a feel for where you are. Most commercial grades of PO4 removers can handle 10,000ppb per 10,000 gallons of pool water per quart of of product administered.
Taylor has the K-1106 phosphate test kit. The Taylor K-1106 test kit can test at phosphate levels of 0-1000 ppm or 0-6000 ppm. It has two different color comparator cards for the two tests.
Using Phosphate Removers
Lanthanum chloride reacts with the free, dissolved phosphate compounds to form a salt (precipitate) of Lanthanum and phosphate (lanthanum phosphate) which is not soluble in water. The chlorine ion from the Lanthanum chloride likely ends up bound to free sodium ions to form sodium chloride, table salt, which would dissolve in water. Lanthanum sulfate is also in these phosphate removers and reacts in a similar way with phosphate.
Lathanum itself is classified as a rare earth element. It's not actually that rare in deposits, it's just fairly difficult to mine and extract, hence why phosphate removers with lanthanum compounds are relatively expensive and largely unnecessary if proper chlorine levels are maintained.
Effects when fighting Algae
When a user already has algae in their pool Phosphate Removers do very little. In fact when testing for phosphates with a green pool the test will result in a false result as quoted
Algae in a Pool will result in a false reading. as displayed on the instructions from the Orenda 10,000
Additionally a user may add a large amount of phosphate remover to the pool only to see phosphates return quickly once the SLAM Process is complete. This is because live algae has phosphates in the cell walls and these phosphates are released once the algae is killed. If a user removes all phosphates from their water before killing the algae there's a chance they'll need to do it again once their water is clear, thus wasting their money.
If you have algae in your pool water forget trying to remove phosphates and focus on using chlorine to kill the algae.
What's the best Brand of Phosphate Remover?
One of the first cons on phosphate removers is the price.
After I purchased a phosphate test kit and found my levels towards the “high” end I started searching for the best phosphate remover to use. I found there to be a rather large difference in quality from my searching. A liter of “Natural Chemistry” will only remove 2000ppb phosphates from a 10,000-gallon pool while a product such as Orenda PR-10000 will remove 10,000ppb phosphates from a 10,000-gallon pool. Both are in the $40 range while the Natural Chemistry is sold as a 2-liter compared to Orenda which is sold as a quart. Regardless the Orenda brand is considerably the better deal……but how costly is it truly to use? For me and our 24,000 gallon pool I started out my phosphates were roughly 1500ppb, so I needed to add roughly 15 ounces or roughly ½ a bottle. Now as expected the pool became cloudy within minutes which cleared up after a day of filtering. After adding this initial dose last year I needed to add another dose once at the start of this season which was another 10 ounces. As I sit today I still have just over 10 ounces remaining even after 2 years of use now. If the pattern continues in our pool this means the initial purchase of a $40-dollar bottle of Orenda phosphate remover will last me roughly 3 seasons and make the product about $13 a season.