Phosphates and Nitrates: How best to keep your water clean and clear!

Hello and welcome! Today I’d like to tell you all about phosphates and nitrates. I’m sure you’ve heard of these at some point, maybe you remember these terms from your high school science class, but what do these words actually mean? Phosphates are naturally occurring compounds that contain phosphorus. You’re probably asking, “how did phosphorus end up in my pool”? Well, there are many ways this can happen actually.

Sources of Phosphates

  • Rain

While it isn’t always the case sometimes phosphorus, typically from air pollution, can enter your pool, which is why it’s always recommended to cover your pool during a storm.

  • Debris

Pretty much any natural debris that can fall into your pool and begin to decompose such as soil, leaves, or any biological waste will leave phosphates behind.

  • Swimmers

People produce sweat and oils, and these end up getting washed into the water. We also tend to have residue and cleaning products on our skin.


Likewise, nitrates are natural compounds formed of nitrogen. However, unlike phosphates nitrates cannot be removed once in your pool. The only way to get rid of nitrates is to either drain your entire pool or remove portions of contaminated water and replace it with clean water until your nitrate level is at a low enough amount to not cause issues. As you may know, nitrates actually come from many of the same sources as phosphates. So instead of repeating much of the same information, I will focus on one specific source: your own backyard!

Sources of Nitrates

  • Wildlife and pets

While we all love animals, they tend to relieve themselves in our yards. And even if you are trying to clean up after them, some residue will always remain and then all it takes is a little help from mother nature, some rain, or perhaps a strong wind, and now all of that residue is in your pool

  • Fertilizers or Manure

Fertilizers from your garden or even your neighbor’s garden often cross-contaminate into your pool water. And Manure from farmland water runoff is extremely common if you live in rural areas

  • Septic Tanks

Waste from damaged septic tanks can seep into your pool. If this is the case, it will quickly become apparent as this will cause a rather massive spike in nitrates.


All this buildup of Phosphates and Nitrates is the ideal food source for all kinds of algae. Such as green, yellow, pink, and black algae, but if you can remove their food source you can quickly kill off any algae! It’s also worth mentioning that if you’re testing your water and you notice that your phosphorous count is too high you can add a chemical called phosphate remover. Which can be added as a way to prevent algae from ever taking hold if you haven’t seen any signs of them in your pool yet. You can purchase phosphate remover at the link at the bottom of the page.

Symptoms of Algae growth taking hold in your pool and what to do

  • Cloudy, Green Water

You’ll know there’s something wrong with your pool when you step out one day and notice your pool has turned a sickly green! This color is actually the algae itself happily gorging itself on the phosphates and nitrates in your pool. Likewise, you might find your water to be cloudy or murky. This can mean algae is in the water or at least on its way, but this is usually a sign of rampant bacteria growth. Which can include nasties like E. Coli! Slippery and slimy surfaces are often an early warning sign that algae or bacteria have begun to take hold in your pool. This can also be caused by something as simple as your water chemistry being a bit off, but either way, you should act quickly to identify the problem. This can easily be dealt with by shocking your pool. And 24 hours later add an amount of algaecide to your pool.

  • Pink and Yellow Colored Debris

Similar to the green algae mentioned above pink growths on the top of your water or yellow patches on the floor of your pool are forms of algae growth, well this is true of yellow algae, but while we refer to pink algae as, well, algae it’s actually a type of bacteria! While these definitely look scary, they can be dealt with in the same way as the rest.

  • Black algae and Pool mold

Pool mold typically takes the form of white clumps floating on the water’s surface. This growth can clog equipment if not quickly taken care of. Now black algae pose the biggest threat to your pool over anything mentioned so far. Typically appears in the form of black patches in porous sections of your pool’s walls. Unlike everything mentioned above, black algae adding algaecide to your pool alone cannot kill it due to its protective layer. This can be dealt with however by scrubbing ALL surfaces in your pool, especially your filter. Then you need to break a chlorine tablet in half and rub the broken tablet directly onto the affected area. Then finally shocking your pool. This process may need to be repeated several times.

So, if while you’re reading this you decide that you are in need of some chemicals to help balance your pool and or fight off any nastiness that might be swimming around in there then we always recommend the Bio-Dex line of products! You can find our complete catalog of those products HERE. And there we have it! Hopefully, you have a better understanding of how chemicals affect your pool and why keeping phosphates and nitrates out is always a good idea. And you should now know what to do in the event that your pool does become contaminated. If you have any questions don't hesitate to reach out.  And as always thank you for reading and have a wonderful day!


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