PO4 spike after phyto dosing

[stevenc23]

Hi All,

I know this has been brought up before but wanted to post my recent experience to potentially help others in case they have same issue.

My phosphates had been stable at 0.15 for months but it spiked to 0.5 within a day. Repeated multiple tests with different lots of reagent and all confirmed the PO4 spike. Nitrate stayed stable at 15, no other changes in water parameters. I had just started to dose phyto (purchased online from well known supplier) at 0.35ml/gallon on my 170 reef so decided to check the phyto as possibility.

Ran phyto through 0.22um filter and Hanna showed 2.7ppm. So heads up if you see a PO4 spike after dosing phyto, it may be the phyto.

Note phyto arrive in good condition on cool day. Good color and no smell. Looks good under microscope. My guess was excess fertilizer in phyto.

Here is pic of test result. It was diluted so need to multiply by 3 to get true value.

 

[EnterName]

That's odd...

You said you added 35mL phyto per gallon into your tank.

1 US gallon ≈ 3,785mL

So the dilution factor is:
0.35mL ÷ 3,785mL ≈ 0.0000925

So the PO₄ increase the phytoplankton could have caused when it's at 2.7ppm is negligible:
2.7ppm × 0.0000925 ≈ 0.00025ppm

I think we need to keep looking for an alternative explanation. To reach a PO₄ increase of 0.50ppm the phytoplankton would have needed PO₄ levels of 0.50ppm × 10,815 ≈ 5,408ppm (or my math is off )

 

[stevenc23]

Math looks good to me. Will investigate further

 

[Reefer1978]

It all depends on who grows your phyto, and how often they collect. If phyto is collected too soon and fertilizer is still present in the solution, your P will go up.

 

[EnterName]

It all depends on who grows your phyto, and how often they collect. If phyto is collected too soon and fertilizer is still present in the solution, your P will go up.

In Guillard's standard F/2 recipe you will have roughly 3.4ppm PO₄ (1mL F/2 per 1L culture). You would need to dose 650mL (0.17gal) phytoplankton per gallon tank to increase PO₄ by 0.50ppm, so I don't think introducing phosphate through phytoplankton dosing is a concern even when freshly fertilized. OP dosed 0.35mL per gallon so that's only something like 0.0003ppm even when the culture was freshly fertilized.

 

[Reefer1978]

In Guillard's standard F/2 recipe you will have roughly 3.4ppm PO₄ (1mL F/2 per 1L culture). You would need to dose 650mL (0.17gal) phytoplankton per gallon tank to increase PO₄ by 0.50ppm, so I don't think introducing phosphate through phytoplankton dosing is a concern even when freshly fertilized. OP dosed 0.35mL per gallon so that's only something like 0.0003ppm even when the culture was freshly fertilized.

Agreed, I was not doubting your math. Also, there's an assumption here that everyone uses Guillard's F/2, but that's an unknown. I was mainly highlighting the possibility as a source.

 

[Kasrift]

It all depends on who grows your phyto, and how often they collect. If phyto is collected too soon and fertilizer is still present in the solution, your P will go up.

This is very true. It's also true that your Hanna checker can be off because it is a colorometer. Essentially, things blocking the light will cause the reading to be off, hence if you dose phyto and then take a reading those phytoplankton particulates will mess up your reading.

 

[stevenc23]

Used a filter to eliminate actual phyto from test samples so that should not interfere. As a follow up added incremental samples of this phyto to clean saltwater and consistently found a 0.2-0.3 incremental rise in PO4 for each ml added to one gallon of water. Thus if one added 1ml/gallon per day of this batch of phyto (which many recommend) that would theoretically raise the PO4 0.15 in a week.

 

[EnterName]

Also, there's an assumption here that everyone uses Guillard's F/2, but that's an unknown.

Fair point. Walne's medium, for example, has more phosphate (about 12.2ppm PO₄ in the culture). You'd still need roughly 160mL (0.04gal) per gallon of tank water to raise PO₄ by 0.50ppm, about 460 times what OP dosed. So the vendor would have to mess up the recipe pretty badly for phyto dosing to show up on a test.

As a follow up added incremental samples of this phyto to clean saltwater and consistently found a 0.2-0.3 incremental rise in PO4 for each ml added to one gallon of water. Thus if one added 1ml/gallon per day of this batch of phyto (which many recommend) that would theoretically raise the PO4 0.15 in a week.

Thanks for testing! But the numbers don't line up with your 2.7ppm reading. A 0.2 - 0.3ppm rise from 1mL in a gallon would mean the phyto contains around 750 - 1,100ppm PO₄, roughly 300 - 400 times what you measured in the filtrate.

It also doesn't match your weekly estimate: 7 days × 0.2 - 0.3ppm would be 1.4 - 2.1ppm, not 0.15ppm. Did you mean 0.02 - 0.03ppm per mL? That would fit the 0.15ppm per week, but then your 0.35mL/gal dose only adds about 0.01ppm, which still can't explain a jump from 0.15 to 0.50 in a day.

 

[stevenc23]

Fair point. Walne's medium, for example, has more phosphate (about 12.2ppm PO₄ in the culture). You'd still need roughly 160mL (0.04gal) per gallon of tank water to raise PO₄ by 0.50ppm, about 460 times what OP dosed. So the vendor would have to mess up the recipe pretty badly for phyto dosing to show up on a test.


Thanks for testing! But the numbers don't line up with your 2.7ppm reading. A 0.2 - 0.3ppm rise from 1mL in a gallon would mean the phyto contains around 750 - 1,100ppm PO₄, roughly 300 - 400 times what you measured in the filtrate.

It also doesn't match your weekly estimate: 7 days × 0.2 - 0.3ppm would be 1.4 - 2.1ppm, not 0.15ppm. Did you mean 0.02 - 0.03ppm per mL? That would fit the 0.15ppm per week, but then your 0.35mL/gal dose only adds about 0.01ppm, which still can't explain a jump from 0.15 to 0.50 in a day.

Yes, I meant 0.02-0.03 per ml, which would be significant if dosed daily.

Yes, still have no explanation for my large one day jump

 

[JonoH]

Did it drop back down after the spike?