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.