Why did my Phosphate plummet to 0.0?

[Lord_Mort]

Hi guys.

Since the new year, my Phosphates have dropped from .05 to .00. The strange thing is, I am actively trying to raise it!

Quick background: This is a 13.5g Nano and it was fishless and therefor not fed anything for about a year (except occasional reef roids for the zoas). Nitrates were 0 and I ended up with a bad case of Bryopsis, Dinos, and bubble algae. After much research, I knew I needed to get my Nitrates and Phosphates up so I added a Sailfin Molly a few weeks ago and have been feeding it every day. I've also added Copepods and I feed 10ml of phyto daily for the past week. I am also dosing 1.5ml/day silicates and trying to raise my alk. (its hovering around 7dkh) Lastly, I'm adding magnesium in an effort to get rid of the Bryopsis.

The tank is looking better but I am a bit confused as to why my phosphates have dropped. (microbial bloom?)

Any advice?

Thanks!

 

[bushdoc]

Could be because your algae are consuming them.

 

[Lord_Mort]

Could be because your algae are consuming them.

I had that thought too but, there is less algae in the tank now than there was a couple of weeks ago.

 

[Hooz]

Phyto consume phosphate and nitrate as well (and are then consumed by the pods). Maybe dial back on the phyto a bit. 10ml for a 13g tank sounds like a lot to me. I dose about 5ml for every 10g in my systems.

 

[Lord_Mort]

Phyto consume phosphate and nitrate as well (and are then consumed by the pods). Maybe dial back on the phyto a bit. 10ml for a 13g tank sounds like a lot to me. I dose about 5ml for every 10g in my systems.

Makes sense. I will try that.
Do you do your phyto every day?

 

[Hooz]

Makes sense. I will try that.
Do you do your phyto every day?

I dose daily... or at least when I remember to.

 

[Lord_Mort]

So... since I am wanting to raise Nitrates and Phosphates in an effort to allow other microorganisms to out-compete the dinos... is now a good time to add a pair of clown fish or would it be better to wait until the algae is gone?

 

[penguinexdeus]

Are you using Hanna for phosphate testing? I recall hearing that silicate dosing for dinos throws the Hanna checker for phosphate accuracy out the window

 

[Randy Holmes-Farley]

Are you using Hanna for phosphate testing? I recall hearing that silicate dosing for dinos throws the Hanna checker for phosphate accuracy out the window

I don't think that is true to a significant extent, but taricha has been studying it.

@taricha

 

[Lord_Mort]

Are you using Hanna for phosphate testing? I recall hearing that silicate dosing for dinos throws the Hanna checker for phosphate accuracy out the window

Yes, I am!

@taricha I would be interested in your current findings. Thanks!

 

[taricha]

I don't think that is true to a significant extent, but taricha has been studying it.

@taricha

Right. Here's what Rick and I measured in 2020, it takes a whole lot of Si to make the hanna PO4 read too high to a degree that anyone should care about.

This is a combo of data from me and @Rick Mathew

Saltwater spiked with different levels of Silica was measured for PO4 with the Hanna ULR P meter.
What is plotted is the difference in the PO4 measured value from its original (zero SiO2) value.
That Rick's (red) and my (blue) data are so closely in agreement given different Si sources etc makes the effect look likely to be real.

Is this a big effect? Not really. Hanna's Low Range Si checker maxes out at 2.00ppm SiO2. I know of no reason why anyone would want more than 2ppm SiO2. There is no evidence of significant interference at or below that range. But it looks like the interference starts around 2ppm SiO2 and becomes significant compared to the uncertainty in the PO4 test by 4ppm SiO2.

But for some reason it keep coming up where people seem to think that a ppm or two of Silica makes Hanna PO4 tests unusable, so after I rechecked again this year (and got same basic results) I asked @Rick Mathew to take another look with multiple different hanna PO4 packets: ULR P, ULR PO4, LR PO4.
None of them looks much different than what we saw in quoted post above.

You can see that the three different hanna packets all give roughly similar result. For ballpark purposes, call it 100:1. For each 0.01ppm PO4 interference, you need about 1ppm SiO2 to generate it.

Some people seemed to think that Si was causing and extra +0.5ppm PO4 or higher, so Rick even ran up the SiO2 to see just how high you had to go to get something like that....

The 100 to 1 seems still a decent ballpark picture, you need somewhere around ~50ppm SiO2 to get +0.5ppm PO4 reading.

 

[Lord_Mort]

I see... So, in your results, the presence of silicates actually cause a HIGHER than normal reading when it comes to phosphates, correct?

If so, this actually has the opposite impact that I was concerned about. I think it's safe to say that even though I am dosing silicates, I can trust my Hannah checker when it says my PO4 is 0.0. Agreed?

 

[taricha]

If so, this actually has the opposite impact that I was concerned about. I think it's safe to say that even though I am dosing silicates, I can trust my Hannah checker when it says my PO4 is 0.0. Agreed?

Agreed.
Lots of things like to consume PO4. There are many reasons for it to go missing

 

[Lord_Mort]

Any experience or advice for adding more bioload at this point? I'm leaning towards waiting since the nuisances are slowly retreating. However, if adding to the bioload has a good chance of beating the problem sooner, why wait?

 

[penguinexdeus]

Right. Here's what Rick and I measured in 2020, it takes a whole lot of Si to make the hanna PO4 read too high to a degree that anyone should care about.


But for some reason it keep coming up where people seem to think that a ppm or two of Silica makes Hanna PO4 tests unusable, so after I rechecked again this year (and got same basic results) I asked @Rick Mathew to take another look with multiple different hanna PO4 packets: ULR P, ULR PO4, LR PO4.
None of them looks much different than what we saw in quoted post above.

You can see that the three different hanna packets all give roughly similar result. For ballpark purposes, call it 100:1. For each 0.01ppm PO4 interference, you need about 1ppm SiO2 to generate it.

Some people seemed to think that Si was causing and extra +0.5ppm PO4 or higher, so Rick even ran up the SiO2 to see just how high you had to go to get something like that....

The 100 to 1 seems still a decent ballpark picture, you need somewhere around ~50ppm SiO2 to get +0.5ppm PO4 reading.

Thanks and good to know. I haven't been paying attention to my phosphate since I was dosing silicates, so now I feel better about testing