Does PO4 fluctuate through the day?

[reefluvrr]

I have been testing my office reef tank PO4 mainly around 4-6 pm after work each day for the last couple weeks. My goal was to have my PO4 drop from 0.24 slowly to 0.1.

I have been using my Hanna ULR tester and I can see my PO4 drop every couple days.
Basically it went something like this. 0.24---0.22---0.18---0.16---0.15---0.16---0.14---0.14---0.12--0.12--0.11---0.10--0.11

Today, instead of measuring the PO4 at 4-6p.m.; I measured it at 9 a.m. and I got a value of 0.15.
I should have remeasured right away, but thought maybe I will remeasure at around 4-6p.m.
Sure enough I measured at 6 p.m. and my PO4 measured at 0.1

I know there is a Standard Deviation in the test kit, but I wonder if other people have experienced something similar?

Could it be like pH fluctuating through the day?

Thanks

 

[Ron Reefman]

It could be. But phosphate is introduced to the tank with food, fish poop and more. And algae takes up phosphates rather quickly as it is one of their required foods (fertilizer). So it makes sense that it could go up and down.

It could also be testing error (both by the test kit and by the operator). You should do the test 2 times in a row and make sure it's not you introducing an error rate into the measurement.

 

[reefluvrr]

ou should do the test 2 times in a row and make sure it's not you introducing an error rate into the measurement.

Yes, I should have....

But phosphate is introduced to the tank with food, fish poop and more

My tank just woke up from the morning cycle, so it had not been fed yet. Was wondering if mechanism responsible for PO4 metabolism affected during the night as well.

Thanks Ron for the input!

 

[Dan_P]

I have been testing my office reef tank PO4 mainly around 4-6 pm after work each day for the last couple weeks. My goal was to have my PO4 drop from 0.24 slowly to 0.1.

I have been using my Hanna ULR tester and I can see my PO4 drop every couple days.
Basically it went something like this. 0.24---0.22---0.18---0.16---0.15---0.16---0.14---0.14---0.12--0.12--0.11---0.10--0.11

Today, instead of measuring the PO4 at 4-6p.m.; I measured it at 9 a.m. and I got a value of 0.15.
I should have remeasured right away, but thought maybe I will remeasure at around 4-6p.m.
Sure enough I measured at 6 p.m. and my PO4 measured at 0.1

I know there is a Standard Deviation in the test kit, but I wonder if other people have experienced something similar?

Could it be like pH fluctuating through the day?

Thanks

The popular advice to check water parameters at the same time every day is a recognition of the fact that concentrations can vary by time of day. Measurement variation does not seem to be the explanation for your observation.

 

[1ByLand2BySea]

PO4 should definitley be checked at the same time of the day for the reasons mentioned above.
But whatever you are doing to lower the PO4 is working to reduce it gradually and safely.

 

[Randy Holmes-Farley Verified Community Expert]

SInce the sources and possible the sinks of phosphate change through the day, like when a fish releases some, there will likely be small changes in phosphate. Might be interesting to track, but I expect the changes are typically very small because phosphate is heavily buffered by the rock and sand.

 

[reefluvrr]

Might be interesting to track, but I expect the changes are typically very small because phosphate is heavily buffered by the rock and sand.

Can you help estimate how small do you think are those changes may be?

 

[csb123]

I found the same sort of fluctuations when I tested 4x a day for a few days. I tested phosphate daily for a month last summer. It is true, that testing the same time of day, does give you the most reliable trends.

 

[reefluvrr]

I found the same sort of fluctuations when I tested 4x a day for a few days.

About how much fluctuation did you remember having during the day?

 

[csb123]

I’ll check last years log..

 

[Randy Holmes-Farley Verified Community Expert]

Can you help estimate how small do you think are those changes may be?

I personally think the variability of test kits is higher than you are likely to see, but do not know for sure. I can't see the up and down being a lot more than 0.02 ppm and may be much less.

 

[reefluvrr]

I personally think the variability of test kits is higher than you are likely to see

Thank you Randy for your input about the up and down during the day likely being about 0.02 or so.

So I can safely assume the fluctuations I am seeing is caused from my test kits.

 

[Randy Holmes-Farley Verified Community Expert]

Thank you Randy for your input about the up and down during the day likely being about 0.02 or so.

So I can safely assume the fluctuations I am seeing is caused from my test kits.

I'm only speculating based on the known daily additions and subtractions, with some sense of how they get spread out and the fact that processes like binding to rock and sand tend to buffer against any phosphate changes.

I'd be interested to hear if that sequence:

0.24---0.22---0.18---0.16---0.15---0.16---0.14---0.14---0.12--0.12--0.11---0.10--0.11

essentially repeats itself on other days.