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Phosphorus, and Why it’s Important to your Pond

by Joe Cadieux on January 24, 2023

Hello fellow pond connoisseurs,

Behold, the third installment of the major chemical players in your pond environment that I’ve posted on this site.   PHOSPHORUS!

Phos for me? Phos for you? No…. it’s Phosphorus!  (not my best, I admit)

Interestingly enough, phosphorus’ name is derived from the Greek word for Lucifer or Morning Star (referring to the planet Mercury). It was so named because phosphorus, in its elemental form, glows or catches fire. This is why it’s used in match heads…..It is extremely volatile.

Anyhoo… We don’t ever have to deal with elemental phosphorus in ponds; instead, we get phosphate (PO4).   Phosphate is important for all life on Earth.  It’s a necessary building block for DNA, RNA, ATP, and cell walls.  All life that we know of needs phosphate, and it is relatively rare in the environment……This of course brings up all the life we do not know about. For instance, the silicon-based life on Janis VI; the Horta I believe they called themselves.  When Captain Kirk and Commander Spock came into contact wi…..um ….. phosphate…..yes…..moving on.

In fact, for a long time, humans gathered phosphate from human and animal teeth, bone and urine (EWWWW!).  It’s now mined in areas where large fossil deposits are found, like ancient sea beds……

Ok, enough of that….. Why is it important?

Phosphate is the most limiting nutrient in freshwater environments.  It is rare, but it packs a HUGE punch.  Varying the amount of phosphate in any aquatic environment will have very large impacts on the overall ecological state of the waterbody.  In fact, most large-scale management strategies are implemented to limit this one molecule from entering any watershed.  If you ever test your water (and you should test your water), any level at or above 0.03ppm is considered high and in need of a change in management strategy. This is why most lake associations, municipalities, and even whole states have banned phosporus-containing lawn fertilizers; as the phosphate easily runs off into streams that eventually empty into lakes.

If you can manage your phosphate input, you are ahead of the game.  Plants use phosphate to build roots, and algae needs it to grow its cell walls and other cell parts, so if we can cycle it out of the pond environment, you will have clear, algae free water.

Many ponds with a planktonic algae (green water) problem are abnormally high in phosphates.  The single celled planktonic algae reproduces extremely rapidly in high phosphate environments and can become very hard to manage.

So where does dissolved phosphate come from?……. BEHOLD!

Poop…..and urine…..and dead stuff….and sometimes it comes in with your source water

Thanks again to the vast internet for the helpful picture……

Looking over the above diagram, you’ll notice how phosphate moves through the environment.  Just like the other elements that I’ve spoken of (listed above) on this blog, phosphorus can be tied up in plants, animals, insects and bottom sediments.  Our job is to store as much phosphorus in the critters as we can.
That means developing and maintaining a healthy, stable ecosystem.

We can also tie up phosphate with flocculating agents.  These products are fantastic at grabbing phosphate and making it inert.  That is, the flocculate does not allow the trapped phosphate to react or be absorbed by anything. Flocculates effectively remove reactive dissolved phosphate from the water column and sink it to the bottom. It also will grab anything that has open phosphate sites in its cell structure. Planktonic algae have these open sites, and are susceptible to flocculates.  The below products will glom the single cell critters together and eventually sink them the the bottom where they will wither and die. (Muah-hahahahaha)……


A lot of times these treatments are temporary, as the problem resides in the bottom sediments and/or a nutrient overload of the whole aquatic system…… I use these products as a part of maintenance programs to help stabilize the pond environment without using algicides or other pesticides. Be sure to read the label to dose correctly for your pond.


Once again, the best answer lies in proper aeration.  Increasing your pond’s ability to sequester and concentrate nutrients (including phosphate) as parts of higher organisms (fish, insects, etc.) is limited only by the space available and the amount of oxygen in the water column.  Higher organisms like fish, frogs, and insects need many times more phosphate to live and grow algae.  The more complex creatures assimilate the phosphate at high rate, outcompeting the algae for this much needed and rare freshwater resource.

Installing a good aerator or aerating fountain will triple the carrying capacity for fish biomass in any aquatic system. Imagine…. three times the amount of fish!  It will also provide oxygen to the tiny creatures (bacteria and insects) that eat the decomposing organic material on the bottom of the pond.  These sediments are a major source of phosphate in the pond environment.  Imagine, ten times the amount of dragonflies!

For watergardens, running the waterfall as often as you can, and performing a good spring cleanout once per year will help tremendously.


Once the phosphate is consumed by the critters on the bottom, they then work their way up the food chain. Small fish eat insects, big fish eat little fish….. Eventually the phosphate (and other concentrated nutrients) is removed from the system through predation or harvesting by you the pond owner (as it is very healthy to harvest fish from a pond ecosystem).  Be active in the management of your pond.  If you truly care for the pond, it will reward you with big fish and a pristine, elegant aesthetic that you and your family and friends can enjoy for generations.

But….. Seriously….. Aerate the water!  You’ll thank me. Here are some good systems….

Aerating Water Fountain

These are just three options of many available on Midwestponds.com , so click around and see what you can find….

Please feel free to ask me any questions that come to mind or to suggest ideas for future topics on this blog.  I am here to help get you the stuff you need and the knowledge that is vital for a clean, healthy pond ecosystem.

Thank you for being interested enough in your pond to learn more about it…..


Senior Biologist



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