Are zero Phosphates really zero Phosphates?

MrGisonni · Dec 3, 2023

My Hanna LR has measured zero for a month now. I have a bit of rowaphos in a mesh bag in a submersible air uv/pump. I haven't changed it in 6+ weeks so I'm sure it's spent. I feed unwashed mysis shrimp and a little reef roids every few days. I have some bubble algae growing, some gracilaria algae and some filamentous green algae growing in the display. Not much at all really. So..... Is my Hanna reagent bad or am I just below Low Reading into Ultra low. I must have some Phosphate right??!!?

Reefer Matt · Dec 3, 2023

MrGisonni said:
My Hanna LR has measured zero for a month now. I have a bit of rowaphos in a mesh bag in a submersible air uv/pump. I haven't changed it in 6+ weeks so I'm sure it's spent. I feed unwashed mysis shrimp and a little reef roids every few days. I have some bubble algae growing, some gracilaria algae and some filamentous green algae growing in the display. Not much at all really. So..... Is my Hanna reagent bad or am I just below Low Reading into Ultra low. I must have some Phosphate right??!!?

I suggest using the Hanna ULR tester if you run low phosphate. The regular low range tester has an accuracy range of +/- .04 ppm. That means your reading of zero could be .04 ppm. The ULR tester has an accuracy range of +/- .02 ppm, and is better suited for low nutrient tanks. Also, the phosphate may be being consumed by the algae.

MrGisonni · Dec 3, 2023

I just saw on another thread and confirmed.... I am not using the marine checker. No wonder.

MrGisonni · Dec 3, 2023

I was using a freshwater checker. No wonder. New ultra low marine checker is on the way

jda · Dec 4, 2023

Since you asked, you can only test for orthophosphate with the new kit. That is only one kind of phosphate, but there are also many other kinds of PHOSPHOROUS which is what the corals are really after, not phosphate.

There is poly/meta phosphate, organically bound phosphates in addition to ortho. Some articles and studies indicate that coral hosts want to use poly and organically bound first. Ortho is usable as a last resort kind of thing.

You will have phosphorous in many forms including many of the phosphates.

Think of po4, or orthophosphate, as a waste product... what is left over after all of the other forms. You can have near zero ortho and have plenty of available phosphorous for everything - the most common situation for this is low po4 tests and algae everywhere.

MrGisonni · Dec 4, 2023

jda said:
Since you asked, you can only test for orthophosphate with the new kit. That is only one kind of phosphate, but there are also many other kinds of PHOSPHOROUS which is what the corals are really after, not phosphate.

There is poly/meta phosphate, organically bound phosphates in addition to ortho. Some articles and studies indicate that coral hosts want to use poly and organically bound first. Ortho is usable as a last resort kind of thing.

You will have phosphorous in many forms including many of the phosphates.

Think of po4, or orthophosphate, as a waste product... what is left over after all of the other forms. You can have near zero ortho and have plenty of available phosphorous for everything - the most common situation for this is low po4 tests and algae everywhere.

Thank you

GARRIGA · Jan 11, 2024

jda said:
Since you asked, you can only test for orthophosphate with the new kit. That is only one kind of phosphate, but there are also many other kinds of PHOSPHOROUS which is what the corals are really after, not phosphate.

There is poly/meta phosphate, organically bound phosphates in addition to ortho. Some articles and studies indicate that coral hosts want to use poly and organically bound first. Ortho is usable as a last resort kind of thing.

You will have phosphorous in many forms including many of the phosphates.

Think of po4, or orthophosphate, as a waste product... what is left over after all of the other forms. You can have near zero ortho and have plenty of available phosphorous for everything - the most common situation for this is low po4 tests and algae everywhere.

Assuming one overfeeds and regardless what test used or what phosphate tested then by mere fact tank is overfed those zero readings should be of no consequence since it's obvious the occupants are consuming/converting? I liken this to ammonia. We likely will never get a ready in a mature tank yet know it's being introduced constantly by feeding and respiration. To zero or not to zero? Does it really matter.

jda · Jan 11, 2024

This requires education and a bit of faith. Some people like numbers and something tangible. In life, almost all of the super important things are not measurable and this is no different. I have no issue with my no3 being clear on Salifert (0.10 on a more precise test) nor po4 being 1-3 ppb, but not everybody is OK with this type of approach. I would argue that more of them should be, but to each their own.

Most all of the best tanks that I have ever seen are heavy import and heavy export with low residual values.

For numbers people, it sometimes helps to tell them that Hach has a Total P test kit. When my Hannah is showing 1-3 ppb of orthophosphate/po4, the Hach shows 8-10 times that amount in total phosphorous. This 8-10x is what you corals are seeing.