Mystery Phosphates

[HDReef]

So I have been battling phosphates for awhile now in my tank and I finally decided to check my water. I started at my saltwater container, it read .1 phosphates. I then checked my RO container, it read .1 phosphates. So I checked the water coming out of my RO unit, it read .12 phosphates. Both the TDS meter on my RO unit and my handheld TDS meter read 0 for the water coming out of the RO unit. Has anyone ever heard of this before. I thought 0 TDS water could not have phosphates? Any help on this would be appreciated. Thanks

 

Darrell

 

P.S. I use a Hanna checker to check my Phosphates

[Coral Hind]

Make sure the tube for the hanna checker is clean. Even fingerprints on the tube can cause it to read higher.

[jaddc]

+1 also rinse the inside with the sample water.

[HDReef]

Make sure the tube for the hanna checker is clean. Even fingerprints on the tube can cause it to read higher.

 

I always wipe down the tube right before I put it in the checker to remove any fingerprints or water that may have gotten on the outside. So I do not think that is the issue.

 

+1 also rinse the inside with the sample water.

 

I rinse it a couple of times with sample water before every test.

 

 

I may pick up a cheap second phosphate test kit to confirm my results but I do not think the tests are incorrect.

[Coral Hind]

Has anyone ever heard of this before. I thought 0 TDS water could not have phosphates?

No, you can have phosphates with a zero TDS reading. You have to remember that the TDS meter and the Hanna meter both have a range of accuracy. So the TDS may not be exactly zero. Phosphate is weakly ionized and it has a low effect on the conductivity of water so you can have low amounts of phosphates even with zero TDS. There just isn't enough to effect the TDS meter. Because phosphate is so weakly ionized it is one of the first to pass through a DI resin bed. I would replace your DI and see then see what you get. People will start to see Phosphate leaking through the DI a good bit before the color changes.

[jaddc]

OK -- so given that you handle the vial correctly, I'd guess that the meter is off, which is a fairly common problem with spectrophotometers. The problem with hanna is that one cannot easily fix the problem.

 

Sorry not to answer your original question. But yes, if your TDS is zero then phosphate should be zero.

[Origami]

So I have been battling phosphates for awhile now in my tank and I finally decided to check my water. I started at my saltwater container, it read .1 phosphates. I then checked my RO container, it read .1 phosphates. So I checked the water coming out of my RO unit, it read .12 phosphates. Both the TDS meter on my RO unit and my handheld TDS meter read 0 for the water coming out of the RO unit. Has anyone ever heard of this before. I thought 0 TDS water could not have phosphates? Any help on this would be appreciated. Thanks

 

Darrell

 

P.S. I use a Hanna checker to check my Phosphates

0.12 ppm < 1 ppm. Your ppm meter probably isn't detecting it.

 

Your DI resin may be exhausted or nearing exhaustion, too.

[jaddc]

No, you can have phosphates with a zero TDS reading. You have to remember that the TDS meter and the Hanna meter both have a range of accuracy. So the TDS may not be exactly zero. Phosphate is weakly ionized and it has a low effect on the conductivity of water so you can have low amounts of phosphates even with zero TDS. There just isn't enough to effect the TDS meter. Because phosphate is so weakly ionized it is one of the first to pass through a DI resin bed. I would replace your DI and see then see what you get. People will start to see Phosphate leaking through the DI a good bit before the color changes.

 

That's right. But practically, a zero TDS reading indicates the general good health of the RO/DI, right? A well maintained system shouldn't selectively leach phosphates, but filter out other impurities. It would leach phosphate and other, more detectable, ions simultaneously.

 

 

 

 

 

[Origami]

That's right. But practically, a zero TDS reading indicates the general good health of the RO/DI, right? A well maintained system shouldn't selectively leach phosphates, but filter out other impurities. It would leach phosphate and other, more detectable, ions simultaneously.

A zero TDS reading indicates general good health of the RO/DI - yes. As for the selective leaching... As DI resin exhausts it will release ions for which it has lower affinity and trade it out for ions with higher affinity for the resin. Consequently, there's an almost selective "burst" of a series of ions that results such as silicates, nitrates, and phosphates.

 

A technical discussion of this can be found here:

http://nzic.org.nz/ChemProcesses/water/13D.pdf

 

This reference lists the order of affinity of certain cations (positively charged ions) as:

Hg++ <Li+ <H+ <Na+ < K+ ≈ NH4+ < Cd++ < Cs+ < Ag+ < Mn++ < Mg++ < Zn++ < Cu++ < Ni++ < Co++ < Ca++ < Sr++ < Pb++ < Al+++ < Fe+++

 

and for certain anions (negatively charged ions) as:

OH- ≈ F- < HCO3- < Cl- < Br- < NO3- < HSO4- < PO4-- < CrO4-- < SO4--

 

So, if there are sulfates in the water (for example), an anion resin that's nearing exhaustion will release the phosphates that it's binding. Likewise, if there's iron ions in the water, a cation resin will release copper.

 

That's why, when TDS climbs, we should begin to think about changing out our DI resin.

[HDReef]

No, you can have phosphates with a zero TDS reading. You have to remember that the TDS meter and the Hanna meter both have a range of accuracy. So the TDS may not be exactly zero. Phosphate is weakly ionized and it has a low effect on the conductivity of water so you can have low amounts of phosphates even with zero TDS. There just isn't enough to effect the TDS meter. Because phosphate is so weakly ionized it is one of the first to pass through a DI resin bed. I would replace your DI and see then see what you get. People will start to see Phosphate leaking through the DI a good bit before the color changes.

 

The resin was changed less than a week ago and I have only ran about 20 gallons through it so it should not be exhausted yet.

 

0.12 ppm < 1 ppm. Your ppm meter probably isn't detecting it.

 

Your DI resin may be exhausted or nearing exhaustion, too.

 

Makes sense to me.

 

So if my meters are reading 0 TDS and I am still getting phosphates with new RO membranes and new resin, the next question is what do I do at this point to reduce the phosphates? I evaporate 3-4 gallons of water a day and with a reading of .1 phosphates on my RO water I am pretty sure that I have narrowed down why I haven't been able to lower my phosphates. I currently have my refugium light 24/7 with cheato, a GFO reactor and have recently added a ATS (though in fairness I haven't got the ATS running as well as I would like yet)

[jaddc]

A zero TDS reading indicates general good health of the RO/DI - yes. As for the selective leaching... As DI resin exhausts it will release ions for which it has lower affinity and trade it out for ions with higher affinity for the resin. Consequently, there's an almost selective "burst" of a series of ions that results such as silicates, nitrates, and phosphates.

 

A technical discussion of this can be found here:

http://nzic.org.nz/C...s/water/13D.pdf

 

This reference lists the order of affinity of certain cations (positively charged ions) as:

Hg++ <Li+ <H+ <Na+ < K+ ≈ NH4+ < Cd++ < Cs+ < Ag+ < Mn++ < Mg++ < Zn++ < Cu++ < Ni++ < Co++ < Ca++ < Sr++ < Pb++ < Al+++ < Fe+++

 

and for certain anions (negatively charged ions) as:

OH- ≈ F- < HCO3- < Cl- < Br- < NO3- < HSO4- < PO4-- < CrO4-- < SO4--

 

So, if there are sulfates in the water (for example), an anion resin that's nearing exhaustion will release the phosphates that it's binding. Likewise, if there's iron ions in the water, a cation resin will release copper.

 

That's why, when TDS climbs, we should begin to think about changing out our DI resin.

 

I'm with you 100% - and "selective" was the wrong word. But it is a 1:1 exchange. In new resin, 10 ions of sulfate and 10 ions of phosphate are captured, no ions reach the TDS meter, and output from the TDS is zero.

 

If the resin is exhausted, then when 10 sulfate and 10 phosphate enter, then 10 sulphate is absorbed which displaces 10 captured phosphate. Additionally, 10 ions of phosphate pass through untouched.

 

So 20 ions of phosphate hit the TDS meter. The TDS does not care what ion is there, it just provides a measurement of how many charged ions are present.

 

I'm just saying that even with our low-grade hobby TDS meters, 0.1 ppm of phosphate is not going to blow through a well maintained RO/DI unit with a TDS zero reading (assuming TDS meter is calibrated and functioning properly).

 

 

 

[jaddc]

So if my meters are reading 0 TDS and I am still getting phosphates with new RO membranes and new resin, the next question is what do I do at this point to reduce the phosphates? I evaporate 3-4 gallons of water a day and with a reading of .1 phosphates on my RO water I am pretty sure that I have narrowed down why I haven't been able to lower my phosphates. I currently have my refugium light 24/7 with cheato, a GFO reactor and have recently added a ATS (though in fairness I haven't got the ATS running as well as I would like yet)

 

Step one is to be confident in your testing. One thing you could do is order standard phosphate solutions. Hach (www.hach.com) offers several standard phosphate solutions and a reasonable cost and I'm sure there are other vendors out there. Once you have confidently identified the problem, then you can go from there.

[Coral Hind]

I'm just saying that even with our low-grade hobby TDS meters, 0.1 ppm of phosphate is not going to blow through a well maintained RO/DI unit with a TDS zero reading (assuming TDS meter is calibrated and functioning properly).

 

Yes it will. A .1 ppm of phosphate would still show up as 0 ppm on the TDS, depending on the unit. A reading of .99 could even show up as 0 ppm, again depending on the unit's scale. Until it reaches the full 1 ppm it might only show up on the TDS meter as 0.

[jaddc]

Yes it will. A .1 ppm of phosphate would still show up as 0 ppm on the TDS, depending on the unit. A reading of .99 could even show up as 0 ppm, again depending on the unit's scale. Until it reaches the full 1 ppm it might only show up on the TDS meter as 0.

 

Ah crap, I see what I did there. Carry on.

 

BUT... the TDS entering the DI resin is somewhere between 10-0 ppm. So as the DI is expired, and phosphate is displaced, that displacement will be higher than 1 ppm.

 

The other possibility is a low quality DI resin that constantly leaches.

Edited August 3, 2012 by jaddc

[Coral Hind]

HDReef, Are you collecting the water straight from the DI tubing into the test tube or collecting it in a contianer first? The container could pollute the sample.

[HDReef]

HDReef, Are you collecting the water straight from the DI tubing into the test tube or collecting it in a contianer first? The container could pollute the sample.

 

I tested water from the container first and then tested water directly from the DI tube to confirm my results

[Origami]

I'm with you 100% - and "selective" was the wrong word. But it is a 1:1 exchange. In new resin, 10 ions of sulfate and 10 ions of phosphate are captured, no ions reach the TDS meter, and output from the TDS is zero.

 

If the resin is exhausted, then when 10 sulfate and 10 phosphate enter, then 10 sulphate is absorbed which displaces 10 captured phosphate. Additionally, 10 ions of phosphate pass through untouched.

 

So 20 ions of phosphate hit the TDS meter. The TDS does not care what ion is there, it just provides a measurement of how many charged ions are present.

 

I'm just saying that even with our low-grade hobby TDS meters, 0.1 ppm of phosphate is not going to blow through a well maintained RO/DI unit with a TDS zero reading (assuming TDS meter is calibrated and functioning properly).

Yes, but (as a couple of us have mentioned and you now realize) you don't have a ppm meter that will detect 0.1 ppm.

 

Remember, it's charge-based, so a -- charge will occupy 2x the "charge-space" of a - ion in the anion resin. It's also a statistical displacement, not absolute.

[HDReef]

So I bought a gallon of distilled water to do a sanity check on. The test showed .02 PO4. I think that this is the final proof needed that I really am getting .1 PO4 out of my RO/DI unit. With the discussions above, this does not seem unreasonable. I am using well water which more than likely is very high in PO4 (the farms that surround me probably add to the problem). So the next question is what should I do about it. Buying water to top off and do water changes is out of the question with the volume of water that I use. I'm thinking that I may give Vodka dosing a try. Any thoughts?

[jaddc]

1) did you test your well water for a comparison? How high are the phosphates going into the rodi?

2) I would put the spring water into your container and measure the phosphates after a period of time to address the possibility of the container leaching phosphates.