Phosphorus ULR and high silicates

[ReefPig]

Hi,

Is it possible that the Phosphorus ULR checker can inadvertently detect silicates when they are at extremely high levels?

I recently added Siporax media to my sump and I know these release very very high levels of silicates for the first couple of weeks.

My checker has been detecting 50+ppb of Phosphorus and like a dummy I've been panicking thinking they are leaching phosphates.
I've done countless water changes, dosed a metric tonne of lanthanum chloride, run so much GFO that it was coming out my ears, yet every test comes back as 50+

After wasting a week chasing the dragon, I got another non-Hanna test kit and it shows 0.

I double checked my checker against a reference solution, as well as my non-hanna test kit, both reported the exact same CORRECT result.
Yet on my actual tank, the results are completely the other end of the scale.

Many thanks

 

[shadesatsetbreak]

Curious about this because I was about to grab some siporax as well. Is there a way to treat the media before it goes into a tank/sump?

 

[ReefPig]

Curious about this because I was about to grab some siporax as well. Is there a way to treat the media before it goes into a tank/sump?

Sera, the company which makes Siporax, also sells a silicate remover media (Sera Silicate Clear).

They say that the silicates are not biologically available to the tank, meaning that it won't cause diatoms etc.
Whether this is true or not I cannot comment.

I rinsed my Siporax for two days in RODI, yet my tank is still very high.

Phosphates are indeed zero it would appear, but Hanna is detecting very very high levels of Phosphorus.

I'd probably say that if this is true, I likely nearly killed my tank through a combination of extreme LC dosing and GFO off the charts.

 

[LC8Sumi]

50ppb is not that much. Also it might be a bad batch of reagent (had that happen before). Testing error can also make up like +-10ppb easily.

 

[ReefPig]

50ppb is not that much. Also it might be a bad batch of reagent (had that happen before). Testing error can also make up like +-10ppb easily.

50ppb is MASSIVE on a tank that had been running at around 2-5ppb for a while.
That’s 0.15ppm PO4.

I’ve used more than 60 tests over the last week chasing the dragon on this thing, over three packs and different batches.

As per my post, I have tested both the Hanna and non-Hanna kit against a known reference solution and they both test accurately and correct.
On my tank however, Hanna is showing 50+ whilst other kits are showing zero.

 

[LC8Sumi]

Okay, you’re right. I’ll just leave this here (Accuracy):

Also something like a dead snail or feeding with reef roids can up these levels in no time. 0.15ppm PO4 is very little amount (even if it sounds like a lot), it’s 0.15mg/l. So it’s “only” 1.5 grams in 1000 liters, which if it was powder it would be a volume of a pea. It’s pretty hard to measure it accuratelly, especially with not colorimeteric tests. It also binds to caco3 as well. So what I’m trying to say it that maybe it’s just a coincidence that you measure it high since adding siporax, and could be related to something else as well.

 

[Spieg]

Not sure about silicates, but my understanding is that if the water turns cloudy when dosing lanthanum chloride , that indicates the presence of Phosphate. Curious if your water turns cloudy when you dose LC, or does it stay clear?

 

[ReefPig]

Thank you all for your input.

This has been going on for a week now, I've an 8 page thread over on a UK forum going through this in detail and everything has been checked and double checked in detail. The last week has been a massive science experiment.

At this stage, I can all but confirm that the Hanna checker is detecting silicates, I just want Hanna to confirm the same, so I can stop stressing out and wasting time chasing the dragon.

 

[Spieg]

Ever thought about calling Hanna?

 

[ReefPig]

Ever thought about calling Hanna?

She's a lovely girl, but I don't have her number

Joking apart, I just emailed their tech support also.

 

[ReefPig]

@Hanna Instruments Hello, can you advise please.
I also emailed tech support and haven't had a reply from them either.

Many thanks,
Dave

 

[serwobow]

The Hanna phosphorous ULR is likely the same test as the Hanna phosphate checker, just with a different label on it. There is a Youtube video on this. And, on the phosphate checker product sheet, silicate is listed as an interfering substance. Based on that product sheet, your hunch is correct. High silicate in your tank will probably give you a false phosphate reading on both the Hanna phosphorous checker and the phosphate checker. And probably on other commercial tests as well.

 

[ReefPig]

The Hanna phosphorous ULR is likely the same test as the Hanna phosphate checker, just with a different label on it. There is a Youtube video on this. And, on the phosphate checker product sheet, silicate is listed as an interfering substance. Based on that product sheet, your hunch is correct. High silicate in your tank will probably give you a false phosphate reading on both the Hanna phosphorous checker and the phosphate checker. And probably on other commercial tests as well.

Thank you very much, would you be kind enough to point me to the product sheet, as I checked the document and couldn't see mention of silicates.

 

[serwobow]

Here is the link, and the key info:

Home

www.hannainstruments.co.uk

PLEASE NOTE:		In some cases, samples may contain other parameters which may interfere with results
Interference may be caused by:		Iron above 50 mg/L Silica above 50 mg/L Silicate above 10 mg/L Copper above 10 mg/L Hydrogen sulphide, arsenate, turbid sample and highly buffered samples also interfere.

 

[ReefPig]

Oh brilliant!

Oh it's the Phosphate LR it's listed against, I only checked the Phosphorus ULR and Phosphate ULR.
It's the same reagent though, so that would make sense that all three of them are affected by all the same conditions.

 

[Stephers]

@Hanna Instruments any chance to chime in on this more? I have a string of people k myself included) dosing silicates to combat dinos and we've all found we have sudden and unexpected higher levels of phosphates with the ULR. Most are keeping between 1 to 3 ppm of silicates, and the link above says it would interfere at 10. I'm wondering if you have any input. Going to try and compare with other phosphate tests.

 

[ReefPig]

@Hanna Instruments any chance to chime in on this more? I have a string of people k myself included) dosing silicates to combat dinos and we've all found we have sudden and unexpected higher levels of phosphates with the ULR. Most are keeping between 1 to 3 ppm of silicates, and the link above says it would interfere at 10. I'm wondering if you have any input. Going to try and compare with other phosphate tests.

Hanna wouldn’t answer me, I contacted them directly through multiple methods (email / phone). Email no reply, phone I was told someone would get back to me, on here they never responded.

I can 100% confirm all Hanna Phosphate checkers are effected by silicates and a few other things at higher concentration.
I have conducted multiple tests with all three checkers available and they all skew the result.

It seems phosphate and silicate are very close to each other from a wavelength perspective and as such, once the levels reach a certain point, it skews the result.

I just wish they were more honest about the limitations, then I wouldn’t have nearly killed my tank dosing LC.

 

[Stephers]

Hanna wouldn’t answer me, I contacted them directly through multiple methods (email / phone). Email no reply, phone I was told someone would get back to me, on here they never responded.

I can 100% confirm all Hanna Phosphate checkers are effected by silicates and a few other things at higher concentration.
I have conducted multiple tests with all three checkers available and they all skew the result.

It seems phosphate and silicate are very close to each other from a wavelength perspective and as such, once the levels reach a certain point, it skews the result.

I just wish they were more honest about the limitations, then I wouldn’t have nearly killed my tank dosing LC.

Thanks for replying. That's disheartening to hear. Silicate dosing has become a very popular and successful thing for dealing with some types of dinos, so this is important information to know if people are using checkers.

Do you remember what brand you tried that read 0 phosphates?

 

[ReefPig]

Thanks for replying. That's disheartening to hear. Silicate dosing has become a very popular and successful thing for dealing with some types of dinos, so this is important information to know if people are using checkers.

Do you remember what brand you tried that read 0 phosphates?

Do you mean what brand are unaffected by silicates?

If so, any that don’t use a photometer or cell. Any that you color match are fine.

 

[taricha]

Was going to make a new thread on hanna PO4 chemistry showing interference with high Silicates, but a search found this one already.

Tip to @Jason mack who brought it up earlier in a dino thread.
I was skeptical, but it seems to be true, and in some cases, it might change how we choose to dose and test etc.

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 don't 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.
The interference is known about, but may be understated...

info in the Standard Methods - PO4 by ascorbic acid...
"b. Interference: Arsenates react with the molybdate reagent to produce a blue color similar to that formed with phosphate. Concentrations as low as 0.1 mg As/L interfere with the phosphate determination. Hexavalent chromium and NO2 interfere to give results about 3% low at concentrations of 1 mg/L and 10 to 15% low at 10 mg/L. Sulfide (Na2S) and silicate do not interfere at concentrations of 1.0 and 10 mg/L."

I'm not sure why we are seeing interference at a lower range than we ought to, but it seems to be the case. @Dan_P pointed out this is not a hanna issue, it's underlying chemistry - and other test kits will probably not avoid it either.

Under what case could it matter? Jason earlier pointed out the fact that Si is dosed sometimes by those trying to encourage diatoms to compete with dinos, and many don't want to test for Si, or get a faulty kit. Then there are certainly some out there that are shooting for PO4 in the 0.05-0.10 range and may only have half or less of that if they are dosing Si without a reliable Si kit.