Experiment: phosphate in rocks

[threebuoys]

This is technical, but it might help in your quest. po4 does not leach out of rock. It unbinds. This might seem the same, but binding has rules and is predictable. The more than you raise po4 in the water, the more the rock/sand binds. The rock and sand will not just release/leach po4 - you have to lower the water column level of po4 for the rock/sand to unbind.

This is a bind and unbind type of deal, not absorb and leach. You can plan an approach to this and the results will follow.

Growing algae will have rules too. Pay attention to the people with their own chemistry forums and folks who have run some of the largest captive reefs on the planet... you cannot remove algae from one place by growing algae in another. Period. Step up your algae consumers in the tank and if you do grow algae in other places without consumers, your waste products can be lower. Usually there are easy answers, just people who do not know how to read them. Please spend a bit on algae consumers or not much will change.

Hey JDA,

I find this interesting. Please help educate me a bit more. Before reading your post, I assumed on R2R the term bind meant absorb and the term unbind meant leach. What's the difference?

Thanks,

 

[jda]

Google and a good science article is going to be better than me... but absorb is things moving into another thing while binding is the process of adhesion with rules.

 

[exnisstech]

This is technical, but it might help in your quest. po4 does not leach out of rock. It unbinds. This might seem the same, but binding has rules and is predictable. The more than you raise po4 in the water, the more the rock/sand binds. The rock and sand will not just release/leach po4 - you have to lower the water column level of po4 for the rock/sand to unbind.

The products remove po4 from the water. The rock/sand then unbinds some. You have to wash, rinse repeat this for a long time to remove all of the po4 from the rocks. ALWAYS change your GFO or Aluminum Oxide when you change water or else po4 can unbind from these too.

Thanks for this explanation.

 

[danimal1211]

As I understand it and I hope to be corrected if I’m wrong is that phosphates are always bound in our arogonite surfaces (rock and sand). They will equalize with the water around them. If the water has a higher P they will absorb until equilibrium. If the water has a lower P they will release it until equilibrium. Aragonite can hold A LOT!! Of PO4. Therefore it takes a lot of GFO or algae or whatever can bind PO4 to pull out that bound P.

I personally have adopted the philosophy that I don’t have a nuisance algae problem, i have a clean up crew problem and in my small system I am the tang.

 

[VintageReefer]

I have 5 Mexican turbos, a fighting conch, and I added 10 scarlet hermits the other day because I wanted some hermits. My cardinal fish and fire fish could care less about algae.

I consider my turf scrubber as my consumer. It put the tank through a cycle of removing phosphate and nitrates from the water column, then the rock releases / unbinds phosphates into the water, then the scrubber removes them. Repeated this a few times until the rocks were clean and the water column is maintained at appropriate levels.

 

[Randy Holmes-Farley]

As I understand it and I hope to be corrected if I’m wrong is that phosphates are always bound in our arogonite surfaces (rock and sand). They will equalize with the water around them. If the water has a higher P they will absorb until equilibrium. If the water has a lower P they will release it until equilibrium. Aragonite can hold A LOT!! Of PO4. Therefore it takes a lot of GFO or algae or whatever can bind PO4 to pull out that bound P.

I personally have adopted the philosophy that I don’t have a nuisance algae problem, i have a clean up crew problem and in my small system I am the tang.

Yes. I cannot show the graphs since they are copyrighted, but this sort of graph explains the idea that at higher concentrations, more phosphate binds.

Figure 4. Comparison of adsorption of phosphate on aragonite andcalcite...

Download scientific diagram | Comparison of adsorption of phosphate on aragonite andcalcite (2 g L − 1 ) in from publication: Adsorption and Desorption of Phosphate on Calcite and Aragonite in Seawater | The adsorption and desorption of phosphate on calcite and aragonite were investigated as a...

www.researchgate.net

 

[Randy Holmes-Farley]

Hey JDA,

I find this interesting. Please help educate me a bit more. Before reading your post, I assumed on R2R the term bind meant absorb and the term unbind meant leach. What's the difference?

Thanks,

I would not get too wound up in the wording and some may be in a grey area anyway, but here's how I see some words:

adsorb means attach to a surface
desorb means the opposite: come off of a surface

absorb means to get inside of
leach would often be the opposite: to come out of the inside of something, but it might include surface adsorbed entities

Bind is the action of an ion or molecule attaching to something. It might be a molecule to a surface or to dissolved material (e.g, a single calcium ion can bind to a single EDTA molecule)

Grey areas would be, for example, a DI resin particle. It has internal surfaces that bind and adsorb and desorb, but a whole grain might be termed to absorb and leach.

 

[VintageReefer]

Personally - to the average person - leach vs unbind is irrelevant. The rock is holding phosphate in some way to achieve equilibrium with the water. Lower the waters levels, and the rock will release - call it leach or unbind - phosphate to achieve new equilibrium.

This write up explains the process using simple analogies

Phosphate flow out of rocks

Many people, when they get use algae scrubbers for the first time, get worried when more (not less) algae starts to grow on their rocks. It seems really strange, especially when nitrate and phosphate have gone lower than before. What is happening is that phosphate is coming out of the rocks...

www.reef2reef.com

 

[jda]

I think that it is pretty important to understand. If po4 could just flow out of rocks at any time, why not just rinse them off or change some water with some power heads blowing at them? It matters. Think small, miss small in this case while that might ok with other things.

 

[mizimmer90]

I think that it is pretty important to understand. If po4 could just flow out of rocks at any time, why not just rinse them off or change some water with some power heads blowing at them? It matters. Think small, miss small in this case while that might ok with other things.

If the water you are rinsing with has lower phosphate than the equilibrated fractions would dictate, then this *would* reduce the concentrations on the rock.

How long it takes to equilibrate also matters though as things are not instantaneous

 

[Randy Holmes-Farley]

I would also claim the distinction between absorb and adsorb is very important in other contexts. Something binding to the surface of, say, a Brute trash can will be very limited in amount because the surface area is relatively small, while something IN the plastic can enter or leave in far larger quantities.

 

[jda]

If the water you are rinsing with has lower phosphate than the equilibrated fractions would dictate, then this *would* reduce the concentrations on the rock.

How long it takes to equilibrate also matters though as things are not instantaneous

The salinity and temperature matter, but some might unbind. It is not like washing latex paint out of a paintbrush, though.

Like if we had a sponge made of aragonite that was soft... it might absorb a lot of water and the po4 might adsorb/bind to the aragonite at the same time. When you squeezed out that aragonite sponge, the water would leach/release but the bound po4 would not.

Again, the words might not be important in this case as long as people understand that there are rules with po4 and that nothing just happens out of chance... you are not unlucky or lucky.

In my tests, 24 hours was enough to get to equilibrium in the water. It was much faster (like hours) with smaller quantities. When taking used/rehomed live rock down to zero, much po4 can unbind in an hour at first, but as we get deeper and deeper into the rock, it can take a week to go from 5 ppb to 1 ppb. This is likely not so much the speed of the unbind as much as it is how hard to get the water down into the core of the rock.

 

[VintageReefer]

I think that it is pretty important to understand. If po4 could just flow out of rocks at any time, why not just rinse them off or change some water with some power heads blowing at them? It matters. Think small, miss small in this case while that might ok with other things.

Would not an underwater object experiencing flow always be in a rinsing process?

I always call the situation phosphate bound rock. Bound. Meaning attached. And to fix it, the natural opposite is to unbind. As the phosphate unbinds from the rock, it leaches into the water. Meaning it drains away from a source, into water.

I don’t really see how it matters which term you use. One term is for the phosphate detaching from rock, and one term is for it being absorbed into the water. They go hand in hand.

 

[danimal1211]

If the water you are rinsing with has lower phosphate than the equilibrated fractions would dictate, then this *would* reduce the concentrations on the rock.

How long it takes to equilibrate also matters though as things are not instantaneous

One work around I had thought of (haven’t tried though) would be if someone wanted to reduce PO4 levels to remove a larger rock or two from system and run them in a tub with an overkill amount of gfo then reintroduce them to the tank. This would seem pretty drastic though.

 

[VintageReefer]

Again, the words might not be important in this case as long as people understand that there are rules with po4 and that nothing just happens out of chance... you are not unlucky or lucky.

I agree. And in my last post I thought you were getting hung up on terms, and I see you were just trying to ensure people understood. That’s all I want also. I’ll sometimes over look a terminology blip to stay on track of the big picture. It doesn’t mean I don’t understand

 

[VintageReefer]

One work around I had thought of (haven’t tried though) would be if someone wanted to reduce PO4 levels to remove a larger rock or two from system and run them in a tub with an overkill amount of gfo then reintroduce them to the tank. This would seem pretty drastic though.

This would work but it would be temporary as they would be clean, then be reintroduced to a system with a higher nutrient level. And they would revert

It would be helpful if you wanted to move problem rock to a new system. But moving back in the same system, would cause them to become phosphate bound again, in time, if other steps are not taken in the tank.

 

[jda]

Another place where this matters is that folks like to post that your substrate or rocks might leach (or leech to some) po4 which is why algae might be out of hand. This cannot happen unless you lower the water concentration of po4. The correct terms, or description, might help somebody spend or focus on the right things to fix an algae issue and thinking that rocks leaching/leeching po4 when they already have 0.40 (or whatever) level of po4 is not really all that helpful.

 

[mizimmer90]

The salinity and temperature matter, but some might unbind. It is not like washing latex paint out of a paintbrush, though.

Like if we had a sponge made of aragonite that was soft... it might absorb a lot of water and the po4 might adsorb/bind to the aragonite at the same time. When you squeezed out that aragonite sponge, the water would leach/release but the bound po4 would not.

Again, the words might not be important in this case as long as people understand that there are rules with po4 and that nothing just happens out of chance... you are not unlucky or lucky.

In my tests, 24 hours was enough to get to equilibrium in the water. It was much faster (like hours) with smaller quantities. When taking used/rehomed live rock down to zero, much po4 can unbind in an hour at first, but as we get deeper and deeper into the rock, it can take a week to go from 5 ppb to 1 ppb. This is likely not so much the speed of the unbind as much as it is how hard to get the water down into the core of the rock.

Yup, this makes sense! If flow of water to the inner rocks is severely limited, things will be locally equilibrated but not with the water column and could take a long time to globally equilibrate.

Also, the diminishing returns over time is all apart of the equilibration: i.e. as things equilibrate, the concentration difference gets smaller and the reaction slows.

Also +1 to the sentiment that science is real and nothing happens by chance lol

 

[mizimmer90]

This would work but it would be temporary as they would be clean, then be reintroduced to a system with a higher nutrient level. And they would revert

It would be helpful if you wanted to move problem rock to a new system. But moving back in the same system, would cause them to become phosphate bound again, in time, if other steps are not taken in the tank.

I don't know the prevalence or concentrations of PO4 bound to rocks but if leaching is an issue, I imagine that successive RODI baths would help (aside from what Randy and JDA brought up about PO4 potentially being deeper in the rocks and not easily equilibrated with the water column)!

 

[jda]

Salinity and temperature matter. RODI did not do anything that I could measure. Water alone does not remove much... you need media or chemicals to really make a dent. I would be shocked if a 100% water change with 0.50 water got down to even 0.49 once everything was back to equilibrium. You can make pretty big dents in the bound phosphate with large doses of LC, but I would not do this in a tank with fish or corals.