Trisodium Phosphate Dosing....Math help

[DrinkinPepsi]

Well I used the planted tank calculator and I mixed 227g Trisodium Phosphate to 3785ML water. Says with potassium phosphate in 100 gal 1 mL will yield .11ppm. Well I dosed .5 and it went to .31 a few night ago and am currently down to .27.

will that calculator be that far off for Trisodium phosphate? I tried to run some math biased on a searches I have don here but I could not wrap my head around it.

 

[rennjidk]

It's probably a testing error. I can't imagine a tank consuming 0.3ppm Po4 in just a few days, unless it's brand new or wall to wall algae. Would you happen to be running some sort of removal media such as GFO at the same time? Also did you confirm it was dosed to .5 via testing, or did you rely on the calculators estimate?

 

[DrinkinPepsi]

It's probably a testing error. I can't imagine a tank consuming 0.3ppm Po4 in just a few days, unless it's brand new or wall to wall algae. Would you happen to be running some sort of removal media such as GFO at the same time? Also did you confirm it was dosed to .5 via testing, or did you rely on the calculators estimate?

Sorry I dosed .5 mL and tank raises from .030ppm to .3. Tested tonight and it's .27

 

[rennjidk]

Sorry I dosed .5 mL and tank raises from .030ppm to .3. Tested tonight and it's .27

The calculator should be accurate, even with tri-sodium phosphate. The potassium phosphate is a little weaker, but it's a negligible amount for your use case. I'm not sure how you dosed what should have been 0.055ppm and ended up at 0.3ppm, but there has to be an error in either creating the solution, or in testing Po4. What are you using to test?

 

[Randy Holmes-Farley]

Lots of potential reasons, including powder measurement errors, phosphate binding to rock and sand, testing errors, water volume estimate being off, etc. it seems plenty close enough.

Why are you raising it so much?

 

[DrinkinPepsi]

Lots of potential reasons, including powder measurement errors, phosphate binding to rock and sand, testing errors, water volume estimate being off, etc. it seems plenty close enough.

Why are you raising it so much?

I have figured out that while dosing silicates the Hanna test results are not accurate.

I was trying to get them to about .1. I'll buy a different phosphate test kit tomorrow and I'll report back.

 

[rennjidk]

I have figured out that while dosing silicates the Hanna test results are not accurate.

I was trying to get them to about .1. I'll buy a different phosphate test kit tomorrow and I'll report back.

Depending on how high you've raised them, that will definitely do it.

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.

 

[Randy Holmes-Farley]

I have figured out that while dosing silicates the Hanna test results are not accurate.

I was trying to get them to about .1. I'll buy a different phosphate test kit tomorrow and I'll report back.

Maybe, but the effect is small,

High Silica interference with PO4 measurement

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...

www.reef2reef.com

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.
The interference is known about, but may be understated...

 

[DrinkinPepsi]

I am dosing Si to try and get rid of these LCA dinos. I pull an ICP-MS sample on the 5th. I could very well be over that 2.0ppm.

Dosing 1.33 ml a day 40-42 baum water glass solution.

 

[taricha]

Dosing 1.33 ml a day 40-42 baum water glass solution.

In what system volume? That might be a lot.

if you want to see about how much SiO2 it takes to make the ULR PO4 test read high and by how much, here's data from 3 different people using multiple Si sources.

Here's what that looks like @Miami Reef . (green stars.) You can see it fits in the area where there is no detectable increase in PO4 measured.

We should probably refer to the interference of SiO2 on phosphate measurements as an interference from SiO2 overdose.
Because there's no good reason to dose amounts of SiO2 high enough to actually cause this effect to appear.

 

[DrinkinPepsi]

100 gallons total.

 

[Randy Holmes-Farley]

Ok, I thought you meant silicate was around 0.1 ppm.