Phosphate levels in new tank setup: different measurements

[Dawsokj1988]

I'm currently cycling my newly setup 200 gallon. It's been up and running for 3 weeks. I'm seeing unusual phosphate readings and have used two different measurement tools to try and verify.

Hanna ULR checker: readings of 30, 40, 50 ppb have been showing up, which makes no sense. The water I used is 0 tds from brs's 6 stage rodi unit. I've tried different reagent packets from different boxes and I'm still producing unusual readings.

Red Sea Phosphate Pro kit: showing up as 0 every time. Clear as clear can be.

Are these test kits testing different types of phosphates? I'm not running my lights if that makes a difference. Is there some sort of phosphate residue from the new equipment's oils that need to be processed? I'm using dry rock that was pre-cured for 3 months using lanthanum chloride before entering the tank.

 

[Randy Holmes-Farley Verified Community Expert]

They are measuring the same thing. Dry rock can easily release some more phosphate to the water, but I do not know which values might be accurate.

 

[sghera64]

Hanna ULR checker: readings of 30, 40, 50 ppb have been showing up, which makes no sense. The water I used is 0 tds from brs's 6 stage rodi unit. I've tried different reagent packets from different boxes and I'm still producing unusual readings.

@Dawsokj1988 I use the Hanna ULR too. I have a question for you about your sample preparation procedure: From the time you add the packet of powdered reagent, how long is it before you press the button to start the 3 minute timer?

 

[Dawsokj1988]

@Dawsokj1988 I use the Hanna ULR too. I have a question for you about your sample preparation procedure: From the time you add the packet of powdered reagent, how long is it before you press the button to start the 3 minute timer?

Well if you use one as well, you know about the limited amount of time we have to pour in the packet, shake for 2 mins, clean off the vial of any hand prints, and then insert in and hold down the button. We have a three minute window to perform all of this, or the machine goes into auto shut down mode. So I'd guess that it's about 2 minutes and 20 seconds that passes before I start the 3 minute count down timer. The checker works fine for my other tank, it's just this newly established tank that's giving me odd readings.

 

[sghera64]

Well if you use one as well, you know about the limited amount of time we have. . . . .

Yes, I know. I've done some experimenting with the ULR and I have an idea for you to try. I've made up Phosphate standards using TSP. What I found is that the 5 minute window from when you finish calibration until the time it takes its reading is not critical.

Try this:
1. ) Fill the other cuvette with tank water and set it aside.
2.) Fill the sample cuvette with water and perform the assay like you normally do.
- Record that number.
3.) Remove the sample cuvette and give it a spin to remove any bubbles clinging to the glass. Then set it aside. Do not empty it.
4.) Turn the ULR checker off and then back on again.
5.) This time use the other cuvette with tank water to calibrate the ULR checker.
6.) Put the sample back into the ULR checker and either wait 2-3 minutes and then press the button quickly, or press and hold the button to start the 3 minute timer.
7.) Record the value you get now - - it might be the same but is probably lower than the first reading.
8.) Repeat steps 4 - 7 | You will likely get nearly the same number as the last time.
9.) Repeat steps 4 - 7 |. Please share back the three numbers you get from these steps.

 

[Dawsokj1988]

Yes, I know. I've done some experimenting with the ULR and I have an idea for you to try. I've made up Phosphate standards using TSP. What I found is that the 5 minute window from when you finish calibration until the time it takes its reading is not critical.

Try this:
1. ) Fill the other cuvette with tank water and set it aside.
2.) Fill the sample cuvette with water and perform the assay like you normally do.
- Record that number.
3.) Remove the sample cuvette and give it a spin to remove any bubbles clinging to the glass. Then set it aside. Do not empty it.
4.) Turn the ULR checker off and then back on again.
5.) This time use the other cuvette with tank water to calibrate the ULR checker.
6.) Put the sample back into the ULR checker and either wait 2-3 minutes and then press the button quickly, or press and hold the button to start the 3 minute timer.
7.) Record the value you get now - - it might be the same but is probably lower than the first reading.
8.) Repeat steps 4 - 7 | You will likely get nearly the same number as the last time.
9.) Repeat steps 4 - 7 |. Please share back the three numbers you get from these steps.

I'll give it a go and let know what I find.

 

[Dawsokj1988]

Yes, I know. I've done some experimenting with the ULR and I have an idea for you to try. I've made up Phosphate standards using TSP. What I found is that the 5 minute window from when you finish calibration until the time it takes its reading is not critical.

Try this:
1. ) Fill the other cuvette with tank water and set it aside.
2.) Fill the sample cuvette with water and perform the assay like you normally do.
- Record that number.
3.) Remove the sample cuvette and give it a spin to remove any bubbles clinging to the glass. Then set it aside. Do not empty it.
4.) Turn the ULR checker off and then back on again.
5.) This time use the other cuvette with tank water to calibrate the ULR checker.
6.) Put the sample back into the ULR checker and either wait 2-3 minutes and then press the button quickly, or press and hold the button to start the 3 minute timer.
7.) Record the value you get now - - it might be the same but is probably lower than the first reading.
8.) Repeat steps 4 - 7 | You will likely get nearly the same number as the last time.
9.) Repeat steps 4 - 7 |. Please share back the three numbers you get from these steps.

All the measurements came out fairly close to each other. I'm still trying to wrap my head around how my phosphates could be so high in a brand new aquarium with nothing added. The only thing I haven't tested is the tropic marine pro salt mix.

 

[sghera64]

All the measurements came out fairly close to each other. I'm still trying to wrap my head around how my phosphates could be so high in a brand new aquarium with nothing added. The only thing I haven't tested is the tropic marine pro salt mix.

If I understand your current situation, you are testing the display tank water which is 3 weeks old containing rock that was cured with lanthanum chloride. Lanthanum chloride does not react with organophosphates. You are seeing inorganic phosphate levels around 40 parts per billion (0.04ppm). It is not clear to us if you have a bare bottom or sand bed.

I am assuming you have no coral or algae in the system to take up and help naturally reduce the inorganic phosphorous levels that you are measuring. I see no reason to doubt the analytical results.

Rock can easily contain organophosphate material that will take time to decompose - - a long time. This will be facilitated with bacteria which breakdown the organophosphates and release them into the water as inorganic phosphate (which you are detecting). Your numbers are actually right where I'd expect them to be. They will drop when coral and other plant-like matter are introduced. If you have your lights on, you might start to see some hair algae.

Have you decided on a nutrient management system yet [algae in refugium, turf scrubber, zeovit, carbon dosing, GFO, water changes]?

 

[Dawsokj1988]

If I understand your current situation, you are testing the display tank water which is 3 weeks old containing rock that was cured with lanthanum chloride. Lanthanum chloride does not react with organophosphates. You are seeing inorganic phosphate levels around 40 parts per billion (0.04ppm). It is not clear to us if you have a bare bottom or sand bed.

I am assuming you have no coral or algae in the system to take up and help naturally reduce the inorganic phosphorous levels that you are measuring. I see no reason to doubt the analytical results.

Rock can easily contain organophosphate material that will take time to decompose - - a long time. This will be facilitated with bacteria which breakdown the organophosphates and release them into the water as inorganic phosphate (which you are detecting). Your numbers are actually right where I'd expect them to be. They will drop when coral and other plant-like matter are introduced. If you have your lights on, you might start to see some hair algae.

Have you decided on a nutrient management system yet [algae in refugium, turf scrubber, zeovit, carbon dosing, GFO, water changes]?

Could you define the differences between organophosphates, inorganic phosphates, and organic phosphates? this is where my lack of a chemistry degree comes into play.

The rocks are dry rocks from Marco rocks, which are mined. I do believe that they leach some level of phosphates, which is why I pre-cured them in salt water for 3 months while occasionally adding LaCl. Are you saying that they're leaching organophosphates, which are now being converted into inorganic phosphates? What would cause the shift from organophosphates to inorganic?

The sand I'm using is tropic edan flakes that I pre-soaked and filtered with a 5 gallon bucket filter mod. The sand bed is about 1 inch, give or take.

I've recently introduced some chaeto to the skimz algae reactor to see if anything happens with the measurements of po4. It's only been a few days so it's too early to tell. The system itself is a hybrid zeo/triton set-up with an automated roll filter, algae reactor, and siporax. I'm just not turning on the lights until I see a decrease in po4.

Do you believe that 80 lbs of marco rock that's been pre-cured for 3 months could be leaching this amount of po4?

 

[sghera64]

Sounds like you understand the differences. Phosphate (PO4---) is a free ion. It is ionic, charged and can bond with other ions (lanthanum, iron to be pulled out of solution). Organophosphates are organic molecules that contain phosphorous (not the same as phosphate). The phosphorous in these molecules and not ionic and is covalently bonded to other atoms (carbon, nitrogen).

I don't know the resolution of the Red Sea phosphate kit, but the Hanna ULR reads down to parts per billion. I'm not surprised that the rock and sand could be contributing to the current phosphate level. I wonder what other reefers think.

*** - What I think is more important than your current numbers, is what happens to them week after week. Do they drop or do they stay the same. With your nutrient control strategy, I'd be surprised if you end up with numbers greater than 30 ppb at steady state. It will probably be lower when you reach a large mass of corals in the system too.

BTW - my PO4 readings with the Hanna ULR are generally between 0-15 ppb. I've always had a little hair and bubble algae in my DT beneath LED lights with T5 supplement. I added a heap of macro algae (Ulva) to my sump 3 weeks ago. My hair algae is completely gone from the DT (don't know when that happened because I didn't miss it) and my bubble algae (valonioa) is losing its green and starting to die off. The ulva has tripled in size over three weeks. Now my PO4 is consistently reading 0-ppb on the Hanna ULR - but corals still look healthy.

 

[Dawsokj1988]

Sounds like you understand the differences. Phosphate (PO4---) is a free ion. It is ionic, charged and can bond with other ions (lanthanum, iron to be pulled out of solution). Organophosphates are organic molecules that contain phosphorous (not the same as phosphate). The phosphorous in these molecules and not ionic and is covalently bonded to other atoms (carbon, nitrogen).

I don't know the resolution of the Red Sea phosphate kit, but the Hanna ULR reads down to parts per billion. I'm not surprised that the rock and sand could be contributing to the current phosphate level. I wonder what other reefers think.

*** - What I think is more important than your current numbers, is what happens to them week after week. Do they drop or do they stay the same. With your nutrient control strategy, I'd be surprised if you end up with numbers greater than 30 ppb at steady state. It will probably be lower when you reach a large mass of corals in the system too.

BTW - my PO4 readings with the Hanna ULR are generally between 0-15 ppb. I've always had a little hair and bubble algae in my DT beneath LED lights with T5 supplement. I added a heap of macro algae (Ulva) to my sump 3 weeks ago. My hair algae is completely gone from the DT (don't know when that happened because I didn't miss it) and my bubble algae (valonioa) is losing its green and starting to die off. The ulva has tripled in size over three weeks. Now my PO4 is consistently reading 0-ppb on the Hanna ULR - but corals still look healthy.

Thanks for the reply and explanation. That's awesome to see the ulva making such a significant impact in your DT. I'm slowly ramping up the export methods, so we'll see where it's at in a few weeks.

 

[Randy Holmes-Farley Verified Community Expert]

Sounds like you understand the differences. Phosphate (PO4---) is a free ion. It is ionic, charged and can bond with other ions (lanthanum, iron to be pulled out of solution). Organophosphates are organic molecules that contain phosphorous (not the same as phosphate). The phosphorous in these molecules and not ionic and is covalently bonded to other atoms (carbon, nitrogen).

Just to be clear, many (most), organic phosphates are ionic as well as covalent. DNA, RNA, ATP, phospholipids, phosphorylated proteins, all are charged on the phosphate oxygen as well as having covalent bonds to other oxygen atoms of the phosphate.

 

[sghera64]

Just to be clear, many (most), organic phosphates are ionic as well as covalent. DNA, RNA, ATP, phospholipids, phosphorylated proteins, all are charged on the phosphate oxygen as well as having covalent bonds to other oxygen atoms of the phosphate.

Thank you for the clarification, Randy.

I have a follow-up question: for those proteins, amino acids and other organic molecules containing ionic forms of phosphorous, to what extent do P-binding methods (lanthanum, GFO, Phosban) work?

 

[Randy Holmes-Farley Verified Community Expert]

Bare solid mineral surfaces (GFO, aluminum oxide, etc.) are pretty good at binding organics from seawater. Lanthanum when still in solution won't, but as it precipitates into lanthanum carbonate and lanthanum phosphate, it can.

The attached phosphate will help them bind to these surfaces, but carboxylic acids already on the organics will also help bind to mineral surfaces.

 

[sghera64]

Bare solid mineral surfaces (GFO, aluminum oxide, etc.) are pretty good at binding organics from seawater. Lanthanum when still in solution won't, but as it precipitates into lanthanum carbonate and lanthanum phosphate, it can.

The attached phosphate will help them bind to these surfaces, but carboxylic acids already on the organics will also help bind to mineral surfaces.

Wow! That's pretty cool. I did not realize that even bulky proteins and other fatty-ionic molecules would bind to these agents.

So, if a charged protein binds to the surface of GFO, does bacteria come along and pull it off? And if not, does the protein or carboxylic acid stay there forever?

Does affinity come in to play where a more preferential ion (say phosphate) displaces the organic one?

 

[Randy Holmes-Farley Verified Community Expert]

Wow! That's pretty cool. I did not realize that even bulky proteins and other fatty-ionic molecules would bind to these agents.

So, if a charged protein binds to the surface of GFO, does bacteria come along and pull it off? And if not, does the protein or carboxylic acid stay there forever?

Does affinity come in to play where a more preferential ion (say phosphate) displaces the organic one?

Displacement can happen, but will be slow for a big macromolecule attached to a surface. The protein on a surface can be modified by enzymes and other reactions, and can still be broken apart, although such reactions can be slower than when fully dissolved.

This dissertation has some nice summaries:

https://elib.suub.uni-bremen.de/edocs/00103871-1.pdf