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 0.35 the phytoplankton would have needed PO₄ levels of 0.35ppm × 10,815 ≈ 3,785ppm (or my math is off )

Little correction (thanks Lasse for pointing this out): I initially calculated for an increase of 0.50ppm but the increase was only 0.35ppm. It still required 3,785ppm PO₄.

 

[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?

 

[JonasRoman]

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.

couldnt it be that the phyto was dead? Mutsnt smell bad as it take some time to decompose.

 

[slingfox]

I once poured 2000ml of highly concentrated phyto into my 125g tank. This is over 45x the dosage in the OP of this thread!

I cultured the phyto myself so it was as fresh and alive and it could be. The result is my phosphates declined when I measured it the next day, and the water was crystal clear similar to how it looks after a large water change. The decline in phosphate was a welcome effect since I had elevated phosphates at the time.

I no longer culture my own phyto but have been thinking of restarting it.

 

[Lasse]

Do you have exactly 170 G water or is it a calculated volume from the measurements of the aquarium?

My experiments with diluting a sample and afterwards try to read with a Checker is not good. Normally you dilute with RODI water - and you will get much lesser salinity that IME can affect the readings.

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 )

The rise was not 0.5 ppm - it was 0.35 ppm (after the addition 0.5 and before the addition 0.15 ppm) but it still not explain the rise.

Sincerely Lasse

 

[fryman]

I once poured 2000ml of highly concentrated phyto into my 125g tank. This is over 45x the dosage in the OP of this thread!

I cultured the phyto myself so it was as fresh and alive and it could be. The result is my phosphates declined when I measured it the next day, and the water was crystal clear similar to how it looks after a large water change. The decline in phosphate was a welcome effect since I had elevated phosphates at the time.

I no longer culture my own phyto but have been thinking of restarting it.

I dose 6-8 liters of a tetraselmis/tisochrysis/chaetoceros mix, every day into my 120gal display. I have dosed up to 20liters at a time. With large doses the water turns green or brown or pink (depending on phyto used) for hours, but by next day is clear again.

I've heard people report nutrient reduction and I get the logic why that could happen, but I do not observe any significant impact on nitrate & phosphate measurements after dosing even large amounts of phyto. Maybe I have too many organisms in my display that consume phyto, since I've done this for years and so phyto doesn't have a chance to multiply.

Or there's some other reason I don't understand.

 

[EnterName]

Do you have exactly 170 G water or is it a calculated volume from the measurements of the aquarium?

My experiments with diluting a sample and afterwards try to read with a Checker is not good. Normally you dilute with RODI water - and you will get much lesser salinity that IME can affect the readings.

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 )

The rise was not 0.5 ppm - it was 0.35 ppm (after the addition 0.5 and before the addition 0.15 ppm) but it still not explain the rise.

Sincerely Lasse

Yepp, my bad the increase was 0.35 not 0.50, but we are still several orders of magnitude away from the explanation so it doesn't matter too much

 

[Reefer1978]

I once poured 2000ml of highly concentrated phyto into my 125g tank. This is over 45x the dosage in the OP of this thread!

I cultured the phyto myself so it was as fresh and alive and it could be. The result is my phosphates declined when I measured it the next day, and the water was crystal clear similar to how it looks after a large water change. The decline in phosphate was a welcome effect since I had elevated phosphates at the time.

I no longer culture my own phyto but have been thinking of restarting it.

I dose 6-8 liters of a tetraselmis/tisochrysis/chaetoceros mix, every day into my 120gal display. I have dosed up to 20liters at a time. With large doses the water turns green or brown or pink (depending on phyto used) for hours, but by next day is clear again.

I've heard people report nutrient reduction and I get the logic why that could happen, but I do not observe any significant impact on nitrate & phosphate measurements after dosing even large amounts of phyto. Maybe I have too many organisms in my display that consume phyto, since I've done this for years and so phyto doesn't have a chance to multiply.

Or there's some other reason I don't understand.

 

[fryman]

lol, good question

I have a low light area and keep flame scallops. Because I like them.

But it's alotta work so I don't really recommend this unless you have specific livestock that needs it.