Ohh I see, if I have phosphates that means the oxygen has already converted phosphorus into phosphate right?
Sort of. Read on...
Most aquarium tests are for phosphate. This is the form plants use.
Phosphorus enters the tank in the fish food (in any of several forms, some are giant molecules) then the organisms in the aquarium (fish, shrimp, snails, and many types of microorganisms) digest the food, and use or excrete the phosphorus combined with other elements.
There will
never be free phosphorus in an aquarium, in an animal body, in a plant, or in a microorganism.
It is ALWAYS combined with something. (Google for images of the reaction of phosphorus with water. Or scroll down to the last picture here:
https://en.wikipedia.org/wiki/Phosphorus )
By the time all the organisms are done with it, phosphorus generally ends up in the tank in the form of PO4, though several other forms are entirely possible. It may pass through several animals and microorganisms before it becomes available to the plants.
No matter what path it follows, the phosphorus in the fish food ends up in the tank as plant fertilizer, or else locked up in a way the plants cannot get it.
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1a)
IF the NO3 source for your tank is ONLY fish food.
No nitrogen in any form in the water, no other nitrogen additives.
THEN you can assume that there is also some phosphorus entering the tank.
Q: Please list everything you are adding to the tank. Does your tap water have chloramine?
2)
IF You are not adding phosphorus in any other form,
THEN the only source of phosphorus is fish food.
Phosphorus in the aquarium from the fish food is in about a 10:1 ratio N

.
3)
If point 1 is true (the only source of nitrogen is fish food)
AND
If point 2 is true (the only source of phosphorus is fish food)
AND You say your NO3 is zero.
Then, I say your plants are using up all the nitrogen and phosphorus that is entering the tank in the form of fish food.
4)
If point 1 is false (there is some other source of nitrogen entering the tank)
OR
If point 2 is false (there is some other source of phosphorus entering the tank)
Then it is impossible to say how much (or how little) phosphorus is in the tank.
There is not usually much, if any, phosphorus in tap water. You can figure this out by looking up a water quality report, if you are on a public water source. Some are better than others about what they report.
As for other sources, you are the one with the labels in hand, you are the one adding them to the tank. You tell us.
What are you adding to the tank? What do the labels say? If you cannot figure it out, then tell us the product, brand name, how much you are adding and how often.