Let’s talk binding of phosphates.

[REEFRIED!]

So please help me understand how this works. I understand that phosphate can bind to rock, and even sand. But I am confused about a few things.

First I have gathered that dry rock tends to bind more phosphate than established rock. That makes sense. But why? Is it because of something used in the manufacturing process? Or is it just because there is no established and mature micro biome on the new rock?

Also please explain how this happens. Does the rock essentially grab phosphate from the water column and hold on to it? And then eventually reach some sort of equilibrium and then release it back into the water column? And I’m assuming it can only bind what’s available in the water column? So let’s say your tank has a level of .08 then the rock can bind that and then leave your tank at 0? Then when more pO4 is available it binds that also? How does this whole thing happen.

The reason I bring this up is that over the last month my phosphate levels have shot up. This is over two different Hannah reagents. Although I guess it’s possible both are bad, but I doubt it.

For months my tank has been around 0.05-.10. I have not changed anything in regards to nutrient import. I feed the same as I have been for a year when I set the tank up. All of the sudden my levels have risen. One test two weeks ago was 0.86. Yesterday it was 0.55. The corals look fine. Actually the best they have ever looked. But what is going on. I understand that I can do a water change to lower which I do every two weeks, but the levels just keep going back up. Is my tank binding phosphates? I want to avoid using anything to correct this. I don’t want to use GFO or especially LC, if I don’t have to.

 

[Randy Holmes-Farley]

Bare calcium carbonate surfaces bind many things from seawater, including phosphate.

If other things are in between the seawater and the calcium carbonate (such as coralline algae, green algae, bacteria, encrusting corals, etc.) then the phosphate cannot as readily exchange and those underlying surfaces are less or not involved in binding and release.

While not exactly technically correct, think of phosphate binding to calcium carbonate as forming a very thin layer of calcium phosphate.

That surface phosphate is in and on/off equilibrium between being attached and being in the water. The more phosphate in the water, the more will be bound.

New bare calcium carbonate can act as a sink for phosphate until that equilibrium is reached. At that point, the only new binding that takes place is when the concentration rises.

It may be the case that the rock and sand in your tank was a sink for a while and no longer is a sink at 0.05 ppm, and thus binds none until phosphate rises, then it binds some more, but you also added more, so the phosphate steadily rises.

 

[REEFRIED!]

Bare calcium carbonate surfaces bind many things from seawater, including phosphate.

If other things are in between the seawater and the calcium carbonate (such as coralline algae, green algae, bacteria, encrusting corals, etc.) then the phosphate cannot as readily exchange and those underlying surfaces are less or not involved in binding and release.

While not exactly technically correct, think of phosphate binding to calcium carbonate as forming a very thin layer of calcium phosphate.

That surface phosphate is in and on/off equilibrium between being attached and being in the water. The more phosphate in the water, the more will be bound.

New bare calcium carbonate can act as a sink for phosphate until that equilibrium is reached. At that point, the only new binding that takes place is when the concentration rises.

It may be the case that the rock and sand in your tank was a sink for a while and no longer is a sink at 0.05 ppm, and thus binds none until phosphate rises, then it binds some more, but you also added more, so the phosphate steadily rises.

Thanks Randy. When you say I added more what do you mean? So if I keep doing what I have been doing in regards to feeding and nutrient export will my phosphate eventually level out? Or will it continue to rise?

 

[Randy Holmes-Farley]

Thanks Randy. When you say I added more what do you mean? So if I keep doing what I have been doing in regards to feeding and nutrient export will my phosphate eventually level out? Or will it continue to rise?

I mean via foods.

If you add more than you export, it will continue to rise.

 

[REEFRIED!]

I mean via foods.

If you add more than you export, it will continue to rise.

Ok that’s what I figured. So from my very basic understanding of this whole process, what happens is that the rock can bind available phosphate. It will eventually reach some equilibrium and be somewhat balanced? Unless more phosphate is suddenly available? I was under the impression that the rock and other surfaces could bind phosphate and hold on to it eventually leeching all of it back to the water.

 

[VintageReefer]

It will bind as much as possible like a sponge and it can do this for months or longer.

Then as you remove phosphate from water, and lower the waters phosphate level, it will release phosphate and return to equilibrium. It will not just leak out on its own unless you are lowering the water column phosphate. Releasing all the bound phosphates is a process that also can take weeks or months depending on your methods.

Many times people have high phosphate, and are doing things to lower it, but the level stays the same or returns to the prior level in a day. The bound phosphate is releasing and returning to the level that is equilibrium.

This will continue to happen until all possible phosphate is released

Your test kits measure what’s available at that moment in the water column but they have no idea how much is built up and stored in the rock waiting to be released

I consistently test and get 0-.02 phosphate. If I truly had zero phosphate my corals would starve. I believe I have achieved a perfect balance of phosphate coming in (food and creature waste) with phosphate consumed (corals) and exported (my algae scrubber) to feed my corals and have near zero leftover in the water or rock. This took a few months to get all the phosphate released from my rock and maybe 2-4 weeks to find tune and get to this point. I prefer this way because it’s natural, safe, and cost effective, and it’s easily adjustable.

There are mixed opinions on how much a scrubber can do, consider it another tool available that can work towards helping a problem. Some people get by with just a skimmer. Others use a skimmer and fuge or other people dose vodka. There’s a number of successful ways to reduce and control phosphates. This is just another tool available

 

[e34stx]

Would dosing CaCo3 powder used for flocculant potentially strip any abundance of po4?

 

[Randy Holmes-Farley]

Ok that’s what I figured. So from my very basic understanding of this whole process, what happens is that the rock can bind available phosphate. It will eventually reach some equilibrium and be somewhat balanced? Unless more phosphate is suddenly available? I was under the impression that the rock and other surfaces could bind phosphate and hold on to it eventually leeching all of it back to the water.

It will bind and hold the roughly same amount in the future unless one tries to lower the phosphate concentration in the water.

It doesn’t just suddenly decide to desorb (come off) at some random time.

 

[Clownfishy]

Just to add to the conversation, what would happen if you took some rock out of an aquarium which had very high phosphate for many years and then let that rock to dry out, then you dumped it in pure RO water. Does the phosphate release the phosphate immediately or does it take time? Just trying to understand how often you would need to change the RO water so it continually pulls out the phosphate from the rock e.g. daily, hourly.
Many thanks

 

[Randy Holmes-Farley]

Just to add to the conversation, what would happen if you took some rock out of an aquarium which had very high phosphate for many years and then let that rock to dry out, then you dumped it in pure RO water. Does the phosphate release the phosphate immediately or does it take time? Just trying to understand how often you would need to change the RO water so it continually pulls out the phosphate from the rock e.g. daily, hourly.
Many thanks

Some will release immediately, and some will take longer if it is in pores.. Some won't desorb at all unless you keep replacing the water to keep the level in it very low.

 

[e34stx]

Would dosing CaCo3 powder used for flocculant potentially strip any abundance of po4?

I’m assuming it will

 

[Randy Holmes-Farley]

I’m assuming it will

I believe tests suggest the effect is small.

 

[e34stx]

I believe tests suggest the effect is small.

Ah ok, thanks

 

[Randy Holmes-Farley]

Ah ok, thanks

Perhaps garf or Dan will chime in as I think that may have done some experiments, at least on sand particles.

@Garf
@Dan_P

 

[Garf]

Perhaps garf or Dan will chime in as I think that may have done some experiments, at least on sand particles.

@Garf
@Dan_P

Wow, looks like I've been doing this for 12 months, don't time fly?

Thread 'Desorbing phosphate from sand with lanthanum.' https://www.reef2reef.com/threads/desorbing-phosphate-from-sand-with-lanthanum.981286/

 

[Dan_P]

Perhaps garf or Dan will chime in as I think that may have done some experiments, at least on sand particles.

@Garf
@Dan_P

Here (#120) is where I compared sand to 200 mesh aragonite powder.

Aragonite Sand And Phosphate Adsorption

Dan whats your opinion on this data repeat pattern I'm seeing tap water is supposed to be variable/high in phosphates and impurities we have so many uncountable rip clean threads all using tap and I give you my word nobody has ever pm'd me or skewered the thread one time in all these years...

www.reef2reef.com

The graph is useful for getting a sense for the amount of calcium carbonate needed to remove phosphate.

 

[Mickey]

Interesting topic. I'm going to read both of the attached threads. My tank has been very high phosphate for many, many years and due to various "issues" tank has had in recent years I decided to try to lower it. I know there are several folks on R2R with beautiful tanks who also have high phosphates. In December level was at 2.5 (Yes, that is 2.5 and not .25) and I've got it down to 1.35 using a diluted mixture of LaCL (Randy's DIY recipe diluted with RODI 1:4), dosing 50 ml over 24 hours continuously.

So far no negative impact on any fish so I don't want to make it any more concentrated since it is working. Tank has been set up since 2004 with a mix of silica and aragonite sand and live rock.

I wonder how long it will take to get down to a steady 0.20?