arragonite sand

[seanb1]

on a package of arragonite sand the package says that it buffers water and adds elements to the water, to what degree?

its well known that silica sand is ok to use in a reef tank without any real dangers, other than breathing the dust from a bag of it.

so if someone asks, what are the real benefits of arragonite, why should someone use it?.

thanks.

 

[Boomer]

It adds those to about zero degree, as far as keeping up levels to where you can even measure it. Matter of fact, when you first put it in it actually un-buffers the tank and lowers the pH , C++ and AlK. That is an old myth behind carbonate sands/gravels to buffer the tank.

About all it is good for, as buffer, is to keep the tank from falling below its pH floor, in the mid-low pH 7's. If the pH gets low enough in the sand it will dissolve some of it but it does not mount to much. It is used mostly as it is more natural and usually is a better media for sand critters, as is it more rounded and has little, if any, sharp corners, which can tear these animals.

 

[reef_doug]

<a href=showthread.php?s=&postid=12223894#post12223894 target=_blank>Originally posted</a> by Boomer
It adds those to about zero degree, as far as keeping up levels to where you can even measure it. Matter of fact, when you first put it in it actually un-buffers the tank and lowers the pH , C++ and AlK. That is an old myth behind carbonate sands/gravels to buffer the tank.

About all it is good for, as buffer, is to keep the tank from falling below its pH floor, in the mid-low pH 7's. If the pH gets low enough in the sand it will dissolve some of it but it does not mount to much. It is used mostly as it is more natural and usually is a better media for sand critters, as is it more rounded and has little, if any, sharp corners, which can tear these animals.

Nicely worded. If the sand starts to buffer, then you have other problems. At least you have a ground floor safety net in the low-mid 7 pH range.

 

[bertoni]

Live rock will provide that same "safety net".

 

[robsee06]

Very interesting...

Robert Fenner and Anthony Calfo have this to say about it in their book, "Reef Invertebrates"

"...Aragonite has a distinct advatage in seawater. It is able to dissolve at a significantly higher PH than calcite, which makes it a much better buffer in the marine aquarium....Aragonite will begin to dissolve, in fact, at a PH over 8.0 while calcite does not readily dissolve until a PH below 8.0!..."

Further...

"...Another very important aspect of live sand maintenance that should be mentioned again is replacement or augmentation. In time, you'll notice that your live sand slowly dissolves...You may even notice that it's buffering ability (maintaining calcium, alkalinity, and PH) is waning. There's no doubt about it...the mineral part of your substrate is dissolving. You will need to replace your sand on an as needed basis..."

I can't find the passage right now, but these guys suggest that you can dissolve a noticeable amount of the sandbed within 12-18 months time.

Perhaps this contradicts what Boomer and Bertoni are suggesting?

I've noticed my 12 month old aragonite sandbed is not as thick as it once was. I assumed this was due to settling. After reading Calfo and Fenner, I wonder if it is something else.

How about some more opinions...

 

[bertoni]

This issue comes up a lot. What happens in our tanks can be very complicated, but the rate of sand disappearance is too small to affect the pH or alkalinity, even if the sand is dissolving, which isn't clear. The issue might be compaction, although there are also bacteria that will dissolve sand, silica or aragonite.

 

[Boomer]

Some logic here

..Aragonite will begin to dissolve, in fact, at a PH over 8.0 while calcite does not readily dissolve until a PH below 8.0!..."

If that was the case those with tanks a 7.8, 7.9 would look like a bowl of milk. Second, the corals, coralline, etc would start to dissolve. I'll have to have a talk with them at IMAC, they are a couple of friends of mine.

I've noticed my 12 month old aragonite sandbed is not as thick as it once was. I assumed this was due to settling.

As Jon has stated compaction. When I see data, that x lbs of sand are added and 1 year later there is x - y lbs of sand I will believe it.

Randy goes into this here

Calcium Carbonate as a Supplement (Aragamight; Liquid Reactor)
http://www.advancedaquarist.com/issues/july2002/chem.htm

 

[Patrick12]

The aragonite will dissolve even in a tank with a normal pH at 8.3 or so. The reason is, there are bacteria in the sandbed and other critters who ingest the sand....sea cucumbers come to mind.....and their localized reactions will go below a pH of 7 and dissolve the sand......but that is why it takes a year or two to notice it much. Also, you will notice that a lot fo aragonite sand starts to clump together and form clods.....same reason. As these bacterial processes occur locally in the sand, they cause the sand to dissolve and fuse together. There is a small amount of buffer released when this happens as well....but don't stop with the CaCO3 additions...IYKWIM.

 

[robsee06]

That's an interesting point Boomer...

If the PH is at a point where aragonite sand will begin dissolving then one can assume our corals would begin to dissolve also.

 

[robsee06]

<a href=showthread.php?s=&postid=12224639#post12224639 target=_blank>Originally posted</a> by Patrick12
The aragonite will dissolve even in a tank with a normal pH at 8.3 or so. The reason is, there are bacteria in the sandbed and other critters who ingest the sand....sea cucumbers come to mind.....and their localized reactions will go below a pH of 7 and dissolve the sand......but that is why it takes a year or two to notice it much. Also, you will notice that a lot fo aragonite sand starts to clump together and form clods.....same reason. As these bacterial processes occur locally in the sand, they cause the sand to dissolve and fuse together. There is a small amount of buffer released when this happens as well....but don't stop with the CaCO3 additions...IYKWIM.

Wouldn't those same bacteria dissolve the coral or at the very least the live rock? Bacteria is everywhere.

 

[Randy Holmes-Farley]

The reason that some sand in a deep sand bed slowly dissolves is because the pH is low deep in the bed due to production of CO2 and possibly other acids in areas not in good equilibrium with the tank water.

That may happen deep in pores in live rock too, but in general it takes organic matter to get in there, and that is much more likely in sand beds where detritus settles down and may get buried for various reasons.

It does not happen on exposed rock, sand, or skeleton surfaces.

 

[robsee06]

So Randy...

Would you say that Calfo's and Fenner's statements concerning sand bed's most certainly dissolving and the need to replenish sandbeds somewhat frequently is accurate or do you think Boomer's post above is more accurate concerning what is going on.

I'm not trying to point out who is right or wrong. I'd just like some clarity as to what is going on.

You guys are awesome!

 

[Randy Holmes-Farley]

Folks that have had sand beds for many years running do sometimes see the need to replenish them somewhat. But any comments about its ability to buffer the tank water and supply calcium, alkalinity and pH in a measurable way where one might notice a decline in that ability is not at all common and probably simply a mistake.

 

[Boomer]

More logic

The aragonite will dissolve even in a tank with a normal pH at 8.3 or so. The reason is, there are bacteria in the sandbed and other critters who ingest the sand..

And if it does or lets say it does, it does not mean it adds anything to the tank water in the form of a buffer. As the sand dissolves, we'll say, it does what: Raises the pH, Alk and Ca++, in that area, which has about zero circulation, which then does what, precip right back out of solution where it was and you get cemented sand.

I'm not saying there is no dissolution of Aragonite, but it will have zero impact on doing anything for pH, Alk or Ca++. So, it is really not doing anything, thus does not buffer the water.

robsee06

Year ago a few of us got together for a discussion on the claims of carbonate sands and gravels buffering the water. We were all surprised but back in 1986 we did not know much. A number of tanks where set up with 2.5 in of media and no bio-load. A number of sands where uses, to include crushed coral, limestone, dolomite and even quartz sand. The sand that had the least effect on pH was quartz. The carbonate sand with the least impact on pH was Puka shells.

Why ? The others are all aragonite, except the Puka shells which are calcite. Why were these better ? Carbonates just do not grow on quartz very well, so they stay in solution. The calcite, it has ample amounts of Mg++, which gives them a poor ability to grow carbonates on the surface. Aragonite has little Mg++ as it does not fit well into the crystal lattice. The same can said for Strontium, it fits well into the lattice of aragonite but not calcite. That is why coral limestone rock, which use to be aragonite, gets converted to calcite and has little Sr, as the aragonite lattice can not stand heat and pressure. And over millions of years the Sr is washed out of the deposit.


All of this has to do with carbonate solution kinetics, not a Dick & Jane subject. Randy discusses it here somewhat.

There was also a control, not media at all, just BB and it had the lest impact on pH. pH drops where form ~ 0.2 pH to 0.50 pH over a week period

Calcium
http://www.advancedaquarist.com/issues/mar2002/chem.htm

 

[robsee06]

Interesting stuff guys...Thanks!

 

[Boomer]

pH drops where form ~ 0.2 pH to 0.50 pH over a week period

Over a 3 week period not 1 week

You're welcome.

 

[seanb1]

ok thanks for all the replys.

so basically the only real use that benefits a reef tank is say oolitic argonite sand that is egg shaped is freindly for sand critters because it has rounded edges, and it is white.

and the claims that it buffers water is false especially in a reef tank because by the time it is able to release its elements its already by far too late, the tank has long since crashed.

 

[bertoni]

Well, actually, the silica sand seems to be fine for many sandbed animals, in practice. Some sharks are said to have an issue, but infauna (animals that live in the sand) don't seem to care much, based on populations counts in some silica and oolitic sandbeds.

 

[zaraemna]

I just bought a used setup tank recently and the PH is about 7.8 to 8.0. I have Calflo's book of coral propagation and read the parts about the argonite sand being a buffer. I bought some and threw it in the tank thinking it was going to raise the PH. I was happy when the sand came because of what it said on the bag too. Any way the PH is still low and the sand didn't help any. I guess the above explanations are why. I thought I was doing good by reading the book.

 

[Randy Holmes-Farley]

zaraemna:

I showed in this article that adding fine calcium carbonate does lower pH a tad:

Calcium Carbonate as a Supplement
http://www.advancedaquarist.com/issues/july2002/chem.htm


from it:

Long before these products came out, I noticed that when adding a large amount of calcium carbonate sand (Southdown aragonite sold at Home Depot) to my tank, the pH dropped immediately on addition. I recently repeated that experiment by adding some AragaMIGHT to my reef tank water (1 teaspoon in ½ gallon of tank water). Within 5 minutes the pH had dropped from 8.22 to 8.14. That drop is not very big, and not likely to be of a concern to anyone by itself. It is, however, indicative of the precipitation of carbonate onto the fresh, bare aragonite crystal surfaces. The precipitate is likely to be a mixture of calcium and magnesium carbonate, so the whole process has resulted in a decline in these ions. The decline is reasonably small (I’d estimate it to be about 0.5 meq/L based on the relationship between pH and alkalinity described previously), and involves a lot more solid per unit volume than would typically be used to supplement a reef tank, but the drop in pH is clearly inconsistent with any net dissolution of carbonate (read alkalinity) from the added material.

Remember that I claimed that the drop in the supersaturation of CaCO3 was halted before it was completely eliminated? The above experiment is evidence of this fact. If the supersaturation had disappeared completely, the alkalinity would have dropped by a factor of about 2. Since it did not, the water is still supersaturated, and the precipitation must have been halted prior to reaching saturation of CaCO3.

Why not just measure calcium and alkalinity in the water before and after addition of solid CaCO3? Unfortunately, the presence of CaCO3 particulates in the water that are delivered with the AragaMIGHT and are not dissolved will confound the interpretation. For example, in an alkalinity determination the pH is steadily dropped to below pH 5. At these low pH values, more of these particulates will dissolve (maybe all of them depending on how fast you do the test). When dissolved, they will be measured as available calcium and alkalinity even though they are not dissolved at normal tank pH. Similar issues may apply to calcium tests where the complexing agents used may promote dissolution of dispersed CaCO3. Consequently, you should not be fooled into thinking that these products can be added directly to a marine aquarium because you measured it and it looks like it works (either in the tank or in a test container).