Phosphate Absorption Rates in Aragonite

[Randy Holmes-Farley Verified Community Expert]

It is certainly possible that a new tank using dead rock may have a higher demand for certain trace elements relative to an older tank. In general, though, many tanks are depleted in certain trace elements, as measured by icp, whether new or old.

 

[KimG]

It is certainly possible that a new tank using dead rock may have a higher demand for certain trace elements relative to an older tank. In general, though, many tanks are depleted in certain trace elements, as measured by icp, whether new or old.

Hi Randy.

Once again, thanks for your help.

If I understood correctly jda posts and results, based on post #62 the 1 pound of rock reached equilibrium with the water at a level of 0.052ppm in the water phase, which would actually be a nice level to have in a reef tank.
To get to that level it absorbed (3.6 mg/l - 0.058 mg/l) x 18.9 l = 67mg of phosphate.

Using one of taricha old posts: https://www.reef2reef.com/threads/e...t-limitation-in-reef-tank.380859/post-4663643

Each cube of brine shrimp has 2.2mg of phosphate. So to reach an equilibrium of 0.058mg/l of phosphate in the water using the same type and amount of rock (1 pound) that jda used, you would need approximately 30 cubes of food before you reached that level. And this is not even counting the biology side of things (the fish will absorb a lot of that phosphate, bacteria growing in the system will also uptake a lot if it and normal algae growth will also absorb part). I know this are very crude measurements and probably quiet off, but probably within the same order of magnitude. (it almost seems to much to be true)

While this is probably not news for many (and probably not to you Randy), the scale at which nutrients are being bound by dry rock is absolutely insane.

Are you aware if there is any "easy" way to measure accurately the levels of trace elements (in a lab setting) in a reef tank? I guess not since even ICP as a hard time with some of them.

 

[Randy Holmes-Farley Verified Community Expert]

Correct there’s no good way to measure except by icp.

 

[taricha]

@KimG here's a great paper...
Adsorption and desorption of phosphate on calcite and aragonite in seawater [google scholar]
compared to the small units we are accustomed to measuring P in (ppb), the aragonite can hold very large amounts.

 

[KimG]

@KimG here's a great paper...
Adsorption and desorption of phosphate on calcite and aragonite in seawater [google scholar]
compared to the small units we are accustomed to measuring P in (ppb), the aragonite can hold very large amounts.

Hi taricha
Thanks. Cool article. It is pretty impressive.
However, as I mentioned, I'm really wandering about all the trace elements that may also be binding to the rock at the same time (and maybe at similar rates).

Regarding the phosphate binding, how much do you think this contributes to the time you and others like #ScottB #mcarroll spend helping people deal with dino issues? Not sure most people that set up a reef with dry rock are aware of it.
Not sure which thread is the longest in the all forum, but that one is probably one of the longest.

 

[taricha]

Not understanding the PO4 mechanics, and the measures people take to lower them, I think is a bigger issue than the actual PO4 numbers.
people measure a small value in the water and see some nuisance and decide that the PO4 number in the water must be too high, so they get way too aggressive about pushing the water nutrients down, but the nuisance may not really care about what's in the water - it may be responding more to stores of very local nutrients in the substrate. Stripping water to pull PO4 out of sand is fraught with complications.

 

[Arthur_Dent]

This thread is super interesting to me.

I have recently added a 40 breeder to my system, bringing total system volume to around 120 gallons. I added about 15 lbs of aragonite fine sand to the 40 breeder. Then I added a few coral rocks after bleaching them out. I'm guessing about ten lbs, because I wanted to go slow on new rock addition.

Didn't measure for a few days, and po4 fell to zero.

I created a solution using trisodium phosphate, that will raise po4 in 120 gallons of water by approximately 0.02ppm for every 1mo added. I doese 5ml of this solution and measured po4. It was pretty close to 0.1 ppm. Within 8 hours, po4 was zero. Dosed another 5ml. Within 8 hours, po4 was zero. Dosed another 5ml last night. Measured around lunch time today, and got zero. Dosed again, but this time only to 0.03 about an hour ago. Measured. Got 0.03. Going to measure before bed and dose back to 0.06 ppm if it's zero again.

Question for the folks here. Given the assumptions in this thread, and what I've outlined above, curious what you think the system will soak up. Also curious how much po4 I should plan on dosing as I add new aragonite rocks (planning to add about 60 lbs, over time).

Additionally, curios as to whether adding rock to a tub and dosing to say 1ppm to let it soak po4 before adding to my system would be a good idea, to minimize soak, and avoid bottoming (and the dinos) the system I'm adding things to.

Wall of text....thanks for reading

 

[Randy Holmes-Farley Verified Community Expert]

This thread is super interesting to me.

I have recently added a 40 breeder to my system, bringing total system volume to around 120 gallons. I added about 15 lbs of aragonite fine sand to the 40 breeder. Then I added a few coral rocks after bleaching them out. I'm guessing about ten lbs, because I wanted to go slow on new rock addition.

Didn't measure for a few days, and po4 fell to zero.

I created a solution using trisodium phosphate, that will raise po4 in 120 gallons of water by approximately 0.02ppm for every 1mo added. I doese 5ml of this solution and measured po4. It was pretty close to 0.1 ppm. Within 8 hours, po4 was zero. Dosed another 5ml. Within 8 hours, po4 was zero. Dosed another 5ml last night. Measured around lunch time today, and got zero. Dosed again, but this time only to 0.03 about an hour ago. Measured. Got 0.03. Going to measure before bed and dose back to 0.06 ppm if it's zero again.

Question for the folks here. Given the assumptions in this thread, and what I've outlined above, curious what you think the system will soak up. Also curious how much po4 I should plan on dosing as I add new aragonite rocks (planning to add about 60 lbs, over time).

Additionally, curios as to whether adding rock to a tub and dosing to say 1ppm to let it soak po4 before adding to my system would be a good idea, to minimize soak, and avoid bottoming (and the dinos) the system I'm adding things to.

Wall of text....thanks for reading

I do not think anyone can even wild guess the amount that will be taken up because it depends highly on the surface area of the calcium carbonate and how much phosphate is already there.

Trial and error is the only way to know how much.

Bear in mind that if you overload rock with too much, you will end up struggling to remove it again. That said, 1 ppm may not overload it. Again, surface area to volume ratio matters, etc.

 

[john90009]

I don’t mean to take this thread off topic or anything, but I started my tank with a lot of dry marco rock and my phopahates are close to bottoming out and the rocks been in the water for 5 months. Do you think the rock is stilll leaching anything or ever did leach anything

 

[Arthur_Dent]

I do not think anyone can even wild guess the amount that will be taken up because it depends highly on the surface area of the calcium carbonate and how much phosphate is already there.

Trial and error is the only way to know how much.

Bear in mind that if you overload rock with too much, you will end up struggling to remove it again. That said, 1 ppm may not overload it. Again, surface area to volume ratio matters, etc.

Thanks, Randy! That makes sense. Too many variables to control.

 

[Garf]

Thanks, Randy! That makes sense. Too many variables to control.

For what it’s worth, I’ve been adding some sand in a mesh bag for a few months, for easy disposal. I don’t really measure it but in my little tank, 3 gigantic spoons of sand per week appears to keep phosphate in check. 4 of these massive spoons reduces phosphate. I only keep phos below 0.25ppm, nothing really low. I add the sand when the sock is dirty to better filter the fines that the sand produces. Seems to be good enough in my tank, and we feed it loads of food.

 

[Arthur_Dent]

For what it’s worth, I’ve been adding some sand in a mesh bag for a few months, for easy disposal. I don’t really measure it but in my little tank, 3 gigantic spoons of sand per week appears to keep phosphate in check. 4 of these massive spoons reduces phosphate. I only keep phos below 0.25ppm, nothing really low. I add the sand when the sock is dirty to better filter the fines that the sand produces. Seems to be good enough in my tank, and we feed it loads of food.

Never really thought about sand as a buffer for phosphate, but this seems to be a reasonable and less aggressive alternative to rowaphos. Thanks for sharing!

I generally have a problem keeping Nitrate and phosphate up in my system. Nitrate hovers around 3ppm, and phosphate between 0.03 and 0.09 for the last year or so. Only fluctuation happened after connecting the new system and adding rock and sand.

I'm reasonably happy with this. I do feed like crazy, but also dose carbon (diy nopox) at 4ml/day. Heavy in/heavy out seems to be working and corals/fish are fat and happy.

 

[Randy Holmes-Farley Verified Community Expert]

For what it’s worth, I’ve been adding some sand in a mesh bag for a few months, for easy disposal. I don’t really measure it but in my little tank, 3 gigantic spoons of sand per week appears to keep phosphate in check. 4 of these massive spoons reduces phosphate. I only keep phos below 0.25ppm, nothing really low. I add the sand when the sock is dirty to better filter the fines that the sand produces. Seems to be good enough in my tank, and we feed it loads of food.

Sounds like a nice procedure!

 

[Dan_P]

Final measurement was 52 ppb in the water. .1594ppm.

57.4 total ppm added yields an absorption of 359x at a ratio of about 5 gallons per 1 pound of Florida-based aragonite. We also know that the aragonite is not likely saturated. Is there anything else to learn from?

@Randy Holmes-Farley just compared these results to Millero paper.

If I understand JDA experiment, 1 lb or 454 g of aragonite sand was exposed to 5 gallons or 19 L of water containing 57 ppm PO4, giving an equilibrium concentration of 0.16 ppm PO4. This means 1111 mg of PO4 was adsorbed by the sand at a rate of 2.4 mg/g or 26 micromole/g at a solution equilibrium concentration of 1.7 micromolar PO4. Millero finds 1 micromole/g adsorbed PO4 at 1 micromolar PO4.

What’s going on?

By the way, results from my small scale work, 3 g sand in 40 mL Instant Ocean are too small by the same factor!!

 

[Randy Holmes-Farley Verified Community Expert]

The effect is really determined by surface area exposed, not grams of substrate, so materials with different surface area per gram will be different.

Phosphate will also be competing with magnesium and organics. Jda used new salt water with little or no organic matter. Not sure what Millero used.

In post 19 of this thread I posted an article and some comparative millero data. Is that the reference you are using?

 

[Cory]

Is there a way we could get a rough estimate if sand is good for po4 reduction or not? If i buy a bag of aragonite and use some hcl to dissolve it then test that sand for po4?

 

[taricha]

Is there a way we could get a rough estimate if sand is good for po4 reduction or not? If i buy a bag of aragonite and use some hcl to dissolve it then test that sand for po4?

I would take two water bottles, put tank water containing some PO4 in them and put a teaspoon of aragonite sand in one, and bubble both bottles with an airline for a few hours to a day.

Test each (filter first to exclude aragonite dust). That seems much easier a result to interpret than trying to dissolve some with acid and figure out what the concentration of released po4 means for binding ability.

 

[jda]

It has been a while, so my memory is probably bad, but temperature (78 bound better than room temperature), salinity, time and especially surface area (and ability to get water to all surfaces - forced in a reactor was significantly better than passive) mattered. Since we had no way to even get close to quantifying surface area in the media that I used (chunky aragonite calcium reactor media), all that I really wanted to show is that the binding is exponential and also can bind A LOT. From what I read and studied, there appeared to be no real way to try and figure out a ratio since we could not determine surface area.

I was also using hobby grade test kits... refractometer, hannah phosphorous test kit, etc. Factor that in.

I have no doubt that sand has more surface area than the media that I used and would likely absorb more. The media that I had was pretty phosphate free - I know that I posted it here somewhere, but it was like a rounding error for any significant volume, even though I could slightly test for it in small water quantities. ...or at least this is what I remember, which could be wrong.

Everybody who uses sand and/or aragonite/calcite/lace rock is using them to bind phosphate whether they know it or not. It is important not to let you aragonite soak it all up for you because some day it won't be able to anymore and you will have TONS of bound po4 to deal with.

After reading all of this, a local friend and like .6 po4 in his 150 or 180g reef with sand. He replaced a lot of the sand and still needed about 10 gallons of GFO over a year to get his phosphate to level out to something like .03, but his corals were doing better and some of his inverts started to spawn and multiply again.

 

[jda]

Is there a way we could get a rough estimate if sand is good for po4 reduction or not? If i buy a bag of aragonite and use some hcl to dissolve it then test that sand for po4?

You should soak the sand in heated saltwater first for a few days and then test po4 to baseline what is in the sand already. If the sand is from the ocean, it should be pretty low. If it is from the shore, more terrestrial phosphate can be bound up in it.

 

[areefer01]

After reading all of this, a local friend and like .6 po4 in his 150 or 180g reef with sand. He replaced a lot of the sand and still needed about 10 gallons of GFO over a year to get his phosphate to level out to something like .03, but his corals were doing better and some of his inverts started to spawn and multiply again.

My Hanna checker flashes 200 at me consistently which means my phosphate is over .6 ppm according to their docs. This is using the HI736 kit. 210 gallon display, 170 lbs dry Pukani, 240 lbs Carib Sea special grade sand substrate, 5 year old mixed reef. Only way I can reliably bring it down is dosing LC based products (phosphate rx working the best). GFO needs a dedicated recator to do anything.

Not sure how I saw this thread today but it is interesting to say the least. I feed heavy though due to anthias which is probably the cause - although I still think the Pukani rock is mostly to blame. Even after soaking in LC baths for a good while.

Need to go back to the start and re-read.